| Message ID | 20240415142436.2545003-11-roberto.sassu@huaweicloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | security: digest_cache LSM | expand |
On Mon Apr 15, 2024 at 5:24 PM EEST, Roberto Sassu wrote: > From: Roberto Sassu <roberto.sassu@huawei.com> > > A desirable goal when doing integrity measurements is that they are done > always in the same order across boots, so that the resulting PCR value > becomes predictable and suitable for sealing policies. However, due to > parallel execution of system services at boot, a deterministic order of > measurements is difficult to achieve. > > The digest_cache LSM is not exempted from this issue. Under the assumption > that only the digest list is measured, and file measurements are omitted if > their digest is found in that digest list, a PCR can be predictable only if > all files belong to the same digest list. Otherwise, it will still be > unpredictable, since files accessed in a non-deterministic order will cause > digest lists to be measured in a non-deterministic order too. > > Overcome this issue, if prefetching is enabled, by searching a digest list > file name in digest_list_dir_lookup_filename() among the entries of the > linked list built by digest_cache_dir_create(). If the file name does not > match, read the digest list to trigger its measurement. Otherwise, also > create a digest cache and return that to the caller. Release the extra > reference of the directory digest cache in digest_cache_new(), since it was > only used for the search and it is not going to be returned. > > Prefetching needs to be explicitly enabled by setting the new > security.dig_prefetch xattr to 1 in the directory containing the digest > lists. The newly introduced function digest_cache_prefetch_requested() > checks first if the DIR_PREFETCH bit is set in dig_owner, otherwise it > reads the xattr. digest_cache_create() sets DIR_PREFETCH in dig_owner, if > prefetching is enabled, before declaring the digest cache as initialized. > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > include/uapi/linux/xattr.h | 3 + > security/digest_cache/dir.c | 55 +++++++++++++++++- > security/digest_cache/internal.h | 11 +++- > security/digest_cache/main.c | 95 +++++++++++++++++++++++++++++++- > security/digest_cache/populate.c | 8 ++- > security/digest_cache/verif.c | 5 +- > 6 files changed, 170 insertions(+), 7 deletions(-) > > diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h > index 8a58cf4bce65..8af33d38d9e8 100644 > --- a/include/uapi/linux/xattr.h > +++ b/include/uapi/linux/xattr.h > @@ -57,6 +57,9 @@ > #define XATTR_DIGEST_LIST_SUFFIX "digest_list" > #define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX > > +#define XATTR_DIG_PREFETCH_SUFFIX "dig_prefetch" > +#define XATTR_NAME_DIG_PREFETCH XATTR_SECURITY_PREFIX XATTR_DIG_PREFETCH_SUFFIX > + > #define XATTR_SELINUX_SUFFIX "selinux" > #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX > > diff --git a/security/digest_cache/dir.c b/security/digest_cache/dir.c > index 7bfcdd5f7ef1..a7d203c15386 100644 > --- a/security/digest_cache/dir.c > +++ b/security/digest_cache/dir.c > @@ -54,6 +54,7 @@ static bool digest_cache_dir_iter(struct dir_context *__ctx, const char *name, > new_entry->seq_num = UINT_MAX; > new_entry->digest_cache = NULL; > mutex_init(&new_entry->digest_cache_mutex); > + new_entry->prefetched = false; > > if (new_entry->name[0] < '0' || new_entry->name[0] > '9') > goto out; > @@ -127,6 +128,7 @@ int digest_cache_dir_create(struct digest_cache *digest_cache, > * @digest_cache: Digest cache > * @digest: Digest to search > * @algo: Algorithm of the digest to search > + * @filename: File name of the digest list to search > * > * This function iterates over the linked list created by > * digest_cache_dir_create() and looks up the digest in the digest cache of > @@ -149,7 +151,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > if (!dir_entry->digest_cache) { > cache = digest_cache_create(dentry, digest_list_path, > digest_cache->path_str, > - dir_entry->name); > + dir_entry->name, false, > + false); > /* Ignore digest caches that cannot be instantiated. */ > if (!cache) { > mutex_unlock(&dir_entry->digest_cache_mutex); > @@ -158,6 +161,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > > /* Consume extra ref. from digest_cache_create(). */ > dir_entry->digest_cache = cache; > + /* Digest list was read, mark entry as prefetched. */ > + dir_entry->prefetched = true; > } > mutex_unlock(&dir_entry->digest_cache_mutex); > > @@ -171,6 +176,54 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > return 0UL; > } > > +/** > + * digest_cache_dir_lookup_filename - Lookup a digest list > + * @dentry: Dentry of the file whose digest list is looked up > + * @digest_list_path: Path structure of the digest list directory > + * @digest_cache: Digest cache > + * @filename: File name of the digest list to search > + * > + * This function iterates over the linked list created by > + * digest_cache_dir_create() and looks up a digest list with a matching file > + * name among the entries. If there is no match, it prefetches (reads) the > + * current digest list. Otherwise, it returns the digest cache pointer from > + * digest_cache_create() to the caller. > + * > + * Return: A digest cache pointer if the digest list if found, NULL otherwise. > + */ > +struct digest_cache * > +digest_cache_dir_lookup_filename(struct dentry *dentry, > + struct path *digest_list_path, > + struct digest_cache *digest_cache, > + char *filename) > +{ > + struct digest_cache *cache; > + struct dir_entry *dir_entry; > + bool filename_found; > + > + list_for_each_entry(dir_entry, &digest_cache->dir_entries, list) { > + mutex_lock(&dir_entry->digest_cache_mutex); > + filename_found = !strcmp(dir_entry->name, filename); > + if (!filename_found && dir_entry->prefetched) { > + mutex_unlock(&dir_entry->digest_cache_mutex); > + continue; > + } > + > + cache = digest_cache_create(dentry, digest_list_path, > + digest_cache->path_str, > + dir_entry->name, false, > + filename_found ? false : true); > + > + dir_entry->prefetched = true; > + mutex_unlock(&dir_entry->digest_cache_mutex); > + > + if (filename_found) > + return cache; > + } > + > + return NULL; > +} > + > /** > * digest_cache_dir_free - Free the stored file list and put digest caches > * @digest_cache: Digest cache > diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h > index b7afca8e04da..c13b35f6b2c0 100644 > --- a/security/digest_cache/internal.h > +++ b/security/digest_cache/internal.h > @@ -17,6 +17,7 @@ > #define INIT_IN_PROGRESS 0 /* Digest cache being initialized. */ > #define INVALID 1 /* Digest cache marked as invalid. */ > #define IS_DIR 2 /* Digest cache created from dir. */ > +#define DIR_PREFETCH 3 /* Prefetching requested for dir. */ > > /** > * struct readdir_callback - Structure to store information for dir iteration > @@ -37,6 +38,7 @@ struct readdir_callback { > * @digest_cache: Digest cache associated to the directory entry > * @digest_cache_mutex: Protects @digest_cache > * @seq_num: Sequence number of the directory entry from file name > + * @prefetched: Whether the digest list has been already prefetched > * @name: File name of the directory entry > * > * This structure represents a directory entry with a digest cache created > @@ -47,6 +49,7 @@ struct dir_entry { > struct digest_cache *digest_cache; > struct mutex digest_cache_mutex; > unsigned int seq_num; > + bool prefetched; > char name[]; > } __packed; > > @@ -205,7 +208,8 @@ digest_cache_from_file_sec(const struct file *file) > /* main.c */ > struct digest_cache *digest_cache_create(struct dentry *dentry, > struct path *digest_list_path, > - char *path_str, char *filename); > + char *path_str, char *filename, > + bool prefetch_req, bool prefetch); > > /* htable.c */ > int digest_cache_htable_init(struct digest_cache *digest_cache, u64 num_digests, > @@ -236,6 +240,11 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > struct path *digest_list_path, > struct digest_cache *digest_cache, u8 *digest, > enum hash_algo algo); > +struct digest_cache * > +digest_cache_dir_lookup_filename(struct dentry *dentry, > + struct path *digest_list_path, > + struct digest_cache *digest_cache, > + char *filename); > void digest_cache_dir_free(struct digest_cache *digest_cache); > > #endif /* _DIGEST_CACHE_INTERNAL_H */ > diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c > index 15f1486610a3..a5616fd07c1d 100644 > --- a/security/digest_cache/main.c > +++ b/security/digest_cache/main.c > @@ -83,6 +83,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) > * @digest_list_path: Path structure of the digest list > * @path_str: Path string of the digest list > * @filename: Digest list file name (can be an empty string) > + * @prefetch_req: Whether prefetching has been requested > + * @prefetch: Whether prefetching of a digest list is being done > * > * This function first locates, from the passed path, the digest list inode > * from which the digest cache will be created or retrieved (if it already > @@ -109,7 +111,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) > */ > struct digest_cache *digest_cache_create(struct dentry *dentry, > struct path *digest_list_path, > - char *path_str, char *filename) > + char *path_str, char *filename, > + bool prefetch_req, bool prefetch) This has enough parameters to consider separate "digest_cache_descriptor" or whatever. In some architectures this is beyond register parameters, which is IMHO good threshold to consider that. This will make e.g. tracing easier as you have to map only one parameter to a known struct to inspect the values. > { > struct path file_path; > struct digest_cache *digest_cache = NULL; > @@ -148,6 +151,16 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > dentry->d_name.name); > goto out; > } > + > + if (prefetch) { > + /* Fine to fail, we are just prefetching. */ > + ret = digest_cache_populate(NULL, digest_list_path, > + path_str, filename); > + pr_debug("Digest list %s/%s %s prefetched\n", > + path_str, filename, > + !ret ? "has been" : "cannot be"); > + goto out; > + } > } > > dig_sec = digest_cache_get_security(inode); > @@ -176,6 +189,11 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > > /* Make the other lock contenders wait until creation complete. */ > set_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags); > + > + /* Set DIR_PREFETCH if prefetching was requested. */ > + if (prefetch_req) > + set_bit(DIR_PREFETCH, &digest_cache->flags); > + > mutex_unlock(&dig_sec->dig_owner_mutex); > > if (S_ISREG(inode->i_mode)) { > @@ -220,6 +238,52 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > return digest_cache; > } > > +/** > + * digest_cache_prefetch_requested - Verify if prefetching is requested > + * @digest_list_path: Path structure of the digest list directory > + * @path_str: Path string of the digest list directory > + * > + * This function verifies whether or not digest list prefetching is requested. > + * If dig_owner exists in the inode security blob, it checks the DIR_PREFETCH > + * bit (faster). Otherwise, it reads the new security.dig_prefetch xattr. > + * > + * Return: True if prefetching is requested, false otherwise. > + */ > +static bool digest_cache_prefetch_requested(struct path *digest_list_path, > + char *path_str) > +{ > + struct digest_cache_security *dig_sec; > + bool prefetch_req = false; > + char prefetch_value; > + struct inode *inode; > + int ret; > + > + inode = d_backing_inode(digest_list_path->dentry); > + dig_sec = digest_cache_get_security(inode); > + if (unlikely(!dig_sec)) > + return false; > + > + mutex_lock(&dig_sec->dig_owner_mutex); > + if (dig_sec->dig_owner) { > + /* Reliable test: DIR_PREFETCH set with dig_owner_mutex held. */ > + prefetch_req = test_bit(DIR_PREFETCH, > + &dig_sec->dig_owner->flags); > + mutex_unlock(&dig_sec->dig_owner_mutex); > + return prefetch_req; > + } > + mutex_unlock(&dig_sec->dig_owner_mutex); > + > + ret = vfs_getxattr(&nop_mnt_idmap, digest_list_path->dentry, > + XATTR_NAME_DIG_PREFETCH, &prefetch_value, 1); > + if (ret == 1 && prefetch_value == '1') { > + pr_debug("Prefetching has been enabled for directory %s\n", > + path_str); > + prefetch_req = true; > + } > + > + return prefetch_req; > +} > + > /** > * digest_cache_new - Retrieve digest list file name and request digest cache > * @dentry: Dentry of the inode for which the digest cache will be used > @@ -230,13 +294,19 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > * with that file name. If security.digest_list is not found, this function > * requests the creation of a digest cache on the parent directory. > * > + * On prefetching, if the default path is a directory and if > + * security.digest_list is found, this function first retrieves the directory > + * digest cache, and then calls digest_cache_dir_lookup_filename() to retrieve > + * the desired digest cache in that directory. > + * > * Return: A new digest cache on success, NULL on error. > */ > static struct digest_cache *digest_cache_new(struct dentry *dentry) > { > char filename[NAME_MAX + 1] = { 0 }; > - struct digest_cache *digest_cache = NULL; > + struct digest_cache *digest_cache = NULL, *found; > struct path default_path; > + bool prefetch_req = false; > int ret; > > ret = kern_path(default_path_str, 0, &default_path); > @@ -273,9 +343,28 @@ static struct digest_cache *digest_cache_new(struct dentry *dentry) > pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n", > XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str, > filename); > + > + if (filename[0]) > + prefetch_req = digest_cache_prefetch_requested(&default_path, > + default_path_str); > create: > + /* On prefetching, retrieve the directory digest cache. */ > digest_cache = digest_cache_create(dentry, &default_path, > - default_path_str, filename); > + default_path_str, > + !prefetch_req ? filename : "", > + prefetch_req, false); > + if (!digest_cache) > + goto out; > + > + if (prefetch_req) { > + /* Find the digest cache with a matching file name. */ > + found = digest_cache_dir_lookup_filename(dentry, &default_path, > + digest_cache, > + filename); > + /* Release ref. to the directory digest cache. */ > + digest_cache_put(digest_cache); > + digest_cache = found; > + } > out: > path_put(&default_path); > return digest_cache; > diff --git a/security/digest_cache/populate.c b/security/digest_cache/populate.c > index 9c2fc2295310..17e7b011c367 100644 > --- a/security/digest_cache/populate.c > +++ b/security/digest_cache/populate.c > @@ -143,6 +143,12 @@ int digest_cache_populate(struct digest_cache *digest_cache, > return ret; > } > > + /* The caller wants just to read digest lists. */ > + if (!digest_cache) { > + ret = 0; > + goto out_vfree; > + } > + > data_len = digest_cache_strip_modsig(data, ret); > > /* Digest list parsers initialize the hash table and add the digests. */ > @@ -151,7 +157,7 @@ int digest_cache_populate(struct digest_cache *digest_cache, > if (ret < 0) > pr_debug("Error parsing digest list %s%s%s, ret: %d\n", > path_str, filename[0] ? "/" : "", filename, ret); > - > +out_vfree: > vfree(data); > return ret; > } > diff --git a/security/digest_cache/verif.c b/security/digest_cache/verif.c > index 04023240d3b4..c42ae93261e2 100644 > --- a/security/digest_cache/verif.c > +++ b/security/digest_cache/verif.c > @@ -33,7 +33,7 @@ static void free_verif(struct digest_cache_verif *verif) > * This function lets a verifier supply verification data about a digest list > * being read to populate the digest cache. > * > - * Return: Zero on success, -ENOMEM if out of memory. > + * Return: Zero on success, -ENOMEM if out of memory, -ENOENT on prefetching. > */ > int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, > size_t size) > @@ -41,6 +41,9 @@ int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, > struct digest_cache *digest_cache = digest_cache_from_file_sec(file); > struct digest_cache_verif *new_verif; > > + if (!digest_cache) > + return -ENOENT; > + > /* > * All allocations must be atomic (non-sleepable) since kprobe does not > * allow otherwise (kprobe is needed for testing). BR, Jarkko
On 4/15/2024 9:42 PM, Jarkko Sakkinen wrote: > On Mon Apr 15, 2024 at 5:24 PM EEST, Roberto Sassu wrote: >> From: Roberto Sassu <roberto.sassu@huawei.com> >> >> A desirable goal when doing integrity measurements is that they are done >> always in the same order across boots, so that the resulting PCR value >> becomes predictable and suitable for sealing policies. However, due to >> parallel execution of system services at boot, a deterministic order of >> measurements is difficult to achieve. >> >> The digest_cache LSM is not exempted from this issue. Under the assumption >> that only the digest list is measured, and file measurements are omitted if >> their digest is found in that digest list, a PCR can be predictable only if >> all files belong to the same digest list. Otherwise, it will still be >> unpredictable, since files accessed in a non-deterministic order will cause >> digest lists to be measured in a non-deterministic order too. >> >> Overcome this issue, if prefetching is enabled, by searching a digest list >> file name in digest_list_dir_lookup_filename() among the entries of the >> linked list built by digest_cache_dir_create(). If the file name does not >> match, read the digest list to trigger its measurement. Otherwise, also >> create a digest cache and return that to the caller. Release the extra >> reference of the directory digest cache in digest_cache_new(), since it was >> only used for the search and it is not going to be returned. >> >> Prefetching needs to be explicitly enabled by setting the new >> security.dig_prefetch xattr to 1 in the directory containing the digest >> lists. The newly introduced function digest_cache_prefetch_requested() >> checks first if the DIR_PREFETCH bit is set in dig_owner, otherwise it >> reads the xattr. digest_cache_create() sets DIR_PREFETCH in dig_owner, if >> prefetching is enabled, before declaring the digest cache as initialized. >> >> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> >> --- >> include/uapi/linux/xattr.h | 3 + >> security/digest_cache/dir.c | 55 +++++++++++++++++- >> security/digest_cache/internal.h | 11 +++- >> security/digest_cache/main.c | 95 +++++++++++++++++++++++++++++++- >> security/digest_cache/populate.c | 8 ++- >> security/digest_cache/verif.c | 5 +- >> 6 files changed, 170 insertions(+), 7 deletions(-) >> >> diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h >> index 8a58cf4bce65..8af33d38d9e8 100644 >> --- a/include/uapi/linux/xattr.h >> +++ b/include/uapi/linux/xattr.h >> @@ -57,6 +57,9 @@ >> #define XATTR_DIGEST_LIST_SUFFIX "digest_list" >> #define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX >> >> +#define XATTR_DIG_PREFETCH_SUFFIX "dig_prefetch" >> +#define XATTR_NAME_DIG_PREFETCH XATTR_SECURITY_PREFIX XATTR_DIG_PREFETCH_SUFFIX >> + >> #define XATTR_SELINUX_SUFFIX "selinux" >> #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX >> >> diff --git a/security/digest_cache/dir.c b/security/digest_cache/dir.c >> index 7bfcdd5f7ef1..a7d203c15386 100644 >> --- a/security/digest_cache/dir.c >> +++ b/security/digest_cache/dir.c >> @@ -54,6 +54,7 @@ static bool digest_cache_dir_iter(struct dir_context *__ctx, const char *name, >> new_entry->seq_num = UINT_MAX; >> new_entry->digest_cache = NULL; >> mutex_init(&new_entry->digest_cache_mutex); >> + new_entry->prefetched = false; >> >> if (new_entry->name[0] < '0' || new_entry->name[0] > '9') >> goto out; >> @@ -127,6 +128,7 @@ int digest_cache_dir_create(struct digest_cache *digest_cache, >> * @digest_cache: Digest cache >> * @digest: Digest to search >> * @algo: Algorithm of the digest to search >> + * @filename: File name of the digest list to search >> * >> * This function iterates over the linked list created by >> * digest_cache_dir_create() and looks up the digest in the digest cache of >> @@ -149,7 +151,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, >> if (!dir_entry->digest_cache) { >> cache = digest_cache_create(dentry, digest_list_path, >> digest_cache->path_str, >> - dir_entry->name); >> + dir_entry->name, false, >> + false); >> /* Ignore digest caches that cannot be instantiated. */ >> if (!cache) { >> mutex_unlock(&dir_entry->digest_cache_mutex); >> @@ -158,6 +161,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, >> >> /* Consume extra ref. from digest_cache_create(). */ >> dir_entry->digest_cache = cache; >> + /* Digest list was read, mark entry as prefetched. */ >> + dir_entry->prefetched = true; >> } >> mutex_unlock(&dir_entry->digest_cache_mutex); >> >> @@ -171,6 +176,54 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, >> return 0UL; >> } >> >> +/** >> + * digest_cache_dir_lookup_filename - Lookup a digest list >> + * @dentry: Dentry of the file whose digest list is looked up >> + * @digest_list_path: Path structure of the digest list directory >> + * @digest_cache: Digest cache >> + * @filename: File name of the digest list to search >> + * >> + * This function iterates over the linked list created by >> + * digest_cache_dir_create() and looks up a digest list with a matching file >> + * name among the entries. If there is no match, it prefetches (reads) the >> + * current digest list. Otherwise, it returns the digest cache pointer from >> + * digest_cache_create() to the caller. >> + * >> + * Return: A digest cache pointer if the digest list if found, NULL otherwise. >> + */ >> +struct digest_cache * >> +digest_cache_dir_lookup_filename(struct dentry *dentry, >> + struct path *digest_list_path, >> + struct digest_cache *digest_cache, >> + char *filename) >> +{ >> + struct digest_cache *cache; >> + struct dir_entry *dir_entry; >> + bool filename_found; >> + >> + list_for_each_entry(dir_entry, &digest_cache->dir_entries, list) { >> + mutex_lock(&dir_entry->digest_cache_mutex); >> + filename_found = !strcmp(dir_entry->name, filename); >> + if (!filename_found && dir_entry->prefetched) { >> + mutex_unlock(&dir_entry->digest_cache_mutex); >> + continue; >> + } >> + >> + cache = digest_cache_create(dentry, digest_list_path, >> + digest_cache->path_str, >> + dir_entry->name, false, >> + filename_found ? false : true); >> + >> + dir_entry->prefetched = true; >> + mutex_unlock(&dir_entry->digest_cache_mutex); >> + >> + if (filename_found) >> + return cache; >> + } >> + >> + return NULL; >> +} >> + >> /** >> * digest_cache_dir_free - Free the stored file list and put digest caches >> * @digest_cache: Digest cache >> diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h >> index b7afca8e04da..c13b35f6b2c0 100644 >> --- a/security/digest_cache/internal.h >> +++ b/security/digest_cache/internal.h >> @@ -17,6 +17,7 @@ >> #define INIT_IN_PROGRESS 0 /* Digest cache being initialized. */ >> #define INVALID 1 /* Digest cache marked as invalid. */ >> #define IS_DIR 2 /* Digest cache created from dir. */ >> +#define DIR_PREFETCH 3 /* Prefetching requested for dir. */ >> >> /** >> * struct readdir_callback - Structure to store information for dir iteration >> @@ -37,6 +38,7 @@ struct readdir_callback { >> * @digest_cache: Digest cache associated to the directory entry >> * @digest_cache_mutex: Protects @digest_cache >> * @seq_num: Sequence number of the directory entry from file name >> + * @prefetched: Whether the digest list has been already prefetched >> * @name: File name of the directory entry >> * >> * This structure represents a directory entry with a digest cache created >> @@ -47,6 +49,7 @@ struct dir_entry { >> struct digest_cache *digest_cache; >> struct mutex digest_cache_mutex; >> unsigned int seq_num; >> + bool prefetched; >> char name[]; >> } __packed; >> >> @@ -205,7 +208,8 @@ digest_cache_from_file_sec(const struct file *file) >> /* main.c */ >> struct digest_cache *digest_cache_create(struct dentry *dentry, >> struct path *digest_list_path, >> - char *path_str, char *filename); >> + char *path_str, char *filename, >> + bool prefetch_req, bool prefetch); >> >> /* htable.c */ >> int digest_cache_htable_init(struct digest_cache *digest_cache, u64 num_digests, >> @@ -236,6 +240,11 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, >> struct path *digest_list_path, >> struct digest_cache *digest_cache, u8 *digest, >> enum hash_algo algo); >> +struct digest_cache * >> +digest_cache_dir_lookup_filename(struct dentry *dentry, >> + struct path *digest_list_path, >> + struct digest_cache *digest_cache, >> + char *filename); >> void digest_cache_dir_free(struct digest_cache *digest_cache); >> >> #endif /* _DIGEST_CACHE_INTERNAL_H */ >> diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c >> index 15f1486610a3..a5616fd07c1d 100644 >> --- a/security/digest_cache/main.c >> +++ b/security/digest_cache/main.c >> @@ -83,6 +83,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) >> * @digest_list_path: Path structure of the digest list >> * @path_str: Path string of the digest list >> * @filename: Digest list file name (can be an empty string) >> + * @prefetch_req: Whether prefetching has been requested >> + * @prefetch: Whether prefetching of a digest list is being done >> * >> * This function first locates, from the passed path, the digest list inode >> * from which the digest cache will be created or retrieved (if it already >> @@ -109,7 +111,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) >> */ >> struct digest_cache *digest_cache_create(struct dentry *dentry, >> struct path *digest_list_path, >> - char *path_str, char *filename) >> + char *path_str, char *filename, >> + bool prefetch_req, bool prefetch) > > > This has enough parameters to consider separate "digest_cache_descriptor" > or whatever. In some architectures this is beyond register parameters, > which is IMHO good threshold to consider that. > > This will make e.g. tracing easier as you have to map only one parameter > to a known struct to inspect the values. Uhm, seems still good (6 parameters). Sure, I can make a structure to encapsulate the parameters, but will be used only for this purpose. Not sure the code understandability will improve. Thanks Roberto >> { >> struct path file_path; >> struct digest_cache *digest_cache = NULL; >> @@ -148,6 +151,16 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, >> dentry->d_name.name); >> goto out; >> } >> + >> + if (prefetch) { >> + /* Fine to fail, we are just prefetching. */ >> + ret = digest_cache_populate(NULL, digest_list_path, >> + path_str, filename); >> + pr_debug("Digest list %s/%s %s prefetched\n", >> + path_str, filename, >> + !ret ? "has been" : "cannot be"); >> + goto out; >> + } >> } >> >> dig_sec = digest_cache_get_security(inode); >> @@ -176,6 +189,11 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, >> >> /* Make the other lock contenders wait until creation complete. */ >> set_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags); >> + >> + /* Set DIR_PREFETCH if prefetching was requested. */ >> + if (prefetch_req) >> + set_bit(DIR_PREFETCH, &digest_cache->flags); >> + >> mutex_unlock(&dig_sec->dig_owner_mutex); >> >> if (S_ISREG(inode->i_mode)) { >> @@ -220,6 +238,52 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, >> return digest_cache; >> } >> >> +/** >> + * digest_cache_prefetch_requested - Verify if prefetching is requested >> + * @digest_list_path: Path structure of the digest list directory >> + * @path_str: Path string of the digest list directory >> + * >> + * This function verifies whether or not digest list prefetching is requested. >> + * If dig_owner exists in the inode security blob, it checks the DIR_PREFETCH >> + * bit (faster). Otherwise, it reads the new security.dig_prefetch xattr. >> + * >> + * Return: True if prefetching is requested, false otherwise. >> + */ >> +static bool digest_cache_prefetch_requested(struct path *digest_list_path, >> + char *path_str) >> +{ >> + struct digest_cache_security *dig_sec; >> + bool prefetch_req = false; >> + char prefetch_value; >> + struct inode *inode; >> + int ret; >> + >> + inode = d_backing_inode(digest_list_path->dentry); >> + dig_sec = digest_cache_get_security(inode); >> + if (unlikely(!dig_sec)) >> + return false; >> + >> + mutex_lock(&dig_sec->dig_owner_mutex); >> + if (dig_sec->dig_owner) { >> + /* Reliable test: DIR_PREFETCH set with dig_owner_mutex held. */ >> + prefetch_req = test_bit(DIR_PREFETCH, >> + &dig_sec->dig_owner->flags); >> + mutex_unlock(&dig_sec->dig_owner_mutex); >> + return prefetch_req; >> + } >> + mutex_unlock(&dig_sec->dig_owner_mutex); >> + >> + ret = vfs_getxattr(&nop_mnt_idmap, digest_list_path->dentry, >> + XATTR_NAME_DIG_PREFETCH, &prefetch_value, 1); >> + if (ret == 1 && prefetch_value == '1') { >> + pr_debug("Prefetching has been enabled for directory %s\n", >> + path_str); >> + prefetch_req = true; >> + } >> + >> + return prefetch_req; >> +} >> + >> /** >> * digest_cache_new - Retrieve digest list file name and request digest cache >> * @dentry: Dentry of the inode for which the digest cache will be used >> @@ -230,13 +294,19 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, >> * with that file name. If security.digest_list is not found, this function >> * requests the creation of a digest cache on the parent directory. >> * >> + * On prefetching, if the default path is a directory and if >> + * security.digest_list is found, this function first retrieves the directory >> + * digest cache, and then calls digest_cache_dir_lookup_filename() to retrieve >> + * the desired digest cache in that directory. >> + * >> * Return: A new digest cache on success, NULL on error. >> */ >> static struct digest_cache *digest_cache_new(struct dentry *dentry) >> { >> char filename[NAME_MAX + 1] = { 0 }; >> - struct digest_cache *digest_cache = NULL; >> + struct digest_cache *digest_cache = NULL, *found; >> struct path default_path; >> + bool prefetch_req = false; >> int ret; >> >> ret = kern_path(default_path_str, 0, &default_path); >> @@ -273,9 +343,28 @@ static struct digest_cache *digest_cache_new(struct dentry *dentry) >> pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n", >> XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str, >> filename); >> + >> + if (filename[0]) >> + prefetch_req = digest_cache_prefetch_requested(&default_path, >> + default_path_str); >> create: >> + /* On prefetching, retrieve the directory digest cache. */ >> digest_cache = digest_cache_create(dentry, &default_path, >> - default_path_str, filename); >> + default_path_str, >> + !prefetch_req ? filename : "", >> + prefetch_req, false); >> + if (!digest_cache) >> + goto out; >> + >> + if (prefetch_req) { >> + /* Find the digest cache with a matching file name. */ >> + found = digest_cache_dir_lookup_filename(dentry, &default_path, >> + digest_cache, >> + filename); >> + /* Release ref. to the directory digest cache. */ >> + digest_cache_put(digest_cache); >> + digest_cache = found; >> + } >> out: >> path_put(&default_path); >> return digest_cache; >> diff --git a/security/digest_cache/populate.c b/security/digest_cache/populate.c >> index 9c2fc2295310..17e7b011c367 100644 >> --- a/security/digest_cache/populate.c >> +++ b/security/digest_cache/populate.c >> @@ -143,6 +143,12 @@ int digest_cache_populate(struct digest_cache *digest_cache, >> return ret; >> } >> >> + /* The caller wants just to read digest lists. */ >> + if (!digest_cache) { >> + ret = 0; >> + goto out_vfree; >> + } >> + >> data_len = digest_cache_strip_modsig(data, ret); >> >> /* Digest list parsers initialize the hash table and add the digests. */ >> @@ -151,7 +157,7 @@ int digest_cache_populate(struct digest_cache *digest_cache, >> if (ret < 0) >> pr_debug("Error parsing digest list %s%s%s, ret: %d\n", >> path_str, filename[0] ? "/" : "", filename, ret); >> - >> +out_vfree: >> vfree(data); >> return ret; >> } >> diff --git a/security/digest_cache/verif.c b/security/digest_cache/verif.c >> index 04023240d3b4..c42ae93261e2 100644 >> --- a/security/digest_cache/verif.c >> +++ b/security/digest_cache/verif.c >> @@ -33,7 +33,7 @@ static void free_verif(struct digest_cache_verif *verif) >> * This function lets a verifier supply verification data about a digest list >> * being read to populate the digest cache. >> * >> - * Return: Zero on success, -ENOMEM if out of memory. >> + * Return: Zero on success, -ENOMEM if out of memory, -ENOENT on prefetching. >> */ >> int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, >> size_t size) >> @@ -41,6 +41,9 @@ int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, >> struct digest_cache *digest_cache = digest_cache_from_file_sec(file); >> struct digest_cache_verif *new_verif; >> >> + if (!digest_cache) >> + return -ENOENT; >> + >> /* >> * All allocations must be atomic (non-sleepable) since kprobe does not >> * allow otherwise (kprobe is needed for testing). > > > BR, Jarkko
On Tue Apr 16, 2024 at 1:34 PM EEST, Roberto Sassu wrote: > On 4/15/2024 9:42 PM, Jarkko Sakkinen wrote: > > On Mon Apr 15, 2024 at 5:24 PM EEST, Roberto Sassu wrote: > >> From: Roberto Sassu <roberto.sassu@huawei.com> > >> > >> A desirable goal when doing integrity measurements is that they are done > >> always in the same order across boots, so that the resulting PCR value > >> becomes predictable and suitable for sealing policies. However, due to > >> parallel execution of system services at boot, a deterministic order of > >> measurements is difficult to achieve. > >> > >> The digest_cache LSM is not exempted from this issue. Under the assumption > >> that only the digest list is measured, and file measurements are omitted if > >> their digest is found in that digest list, a PCR can be predictable only if > >> all files belong to the same digest list. Otherwise, it will still be > >> unpredictable, since files accessed in a non-deterministic order will cause > >> digest lists to be measured in a non-deterministic order too. > >> > >> Overcome this issue, if prefetching is enabled, by searching a digest list > >> file name in digest_list_dir_lookup_filename() among the entries of the > >> linked list built by digest_cache_dir_create(). If the file name does not > >> match, read the digest list to trigger its measurement. Otherwise, also > >> create a digest cache and return that to the caller. Release the extra > >> reference of the directory digest cache in digest_cache_new(), since it was > >> only used for the search and it is not going to be returned. > >> > >> Prefetching needs to be explicitly enabled by setting the new > >> security.dig_prefetch xattr to 1 in the directory containing the digest > >> lists. The newly introduced function digest_cache_prefetch_requested() > >> checks first if the DIR_PREFETCH bit is set in dig_owner, otherwise it > >> reads the xattr. digest_cache_create() sets DIR_PREFETCH in dig_owner, if > >> prefetching is enabled, before declaring the digest cache as initialized. > >> > >> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > >> --- > >> include/uapi/linux/xattr.h | 3 + > >> security/digest_cache/dir.c | 55 +++++++++++++++++- > >> security/digest_cache/internal.h | 11 +++- > >> security/digest_cache/main.c | 95 +++++++++++++++++++++++++++++++- > >> security/digest_cache/populate.c | 8 ++- > >> security/digest_cache/verif.c | 5 +- > >> 6 files changed, 170 insertions(+), 7 deletions(-) > >> > >> diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h > >> index 8a58cf4bce65..8af33d38d9e8 100644 > >> --- a/include/uapi/linux/xattr.h > >> +++ b/include/uapi/linux/xattr.h > >> @@ -57,6 +57,9 @@ > >> #define XATTR_DIGEST_LIST_SUFFIX "digest_list" > >> #define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX > >> > >> +#define XATTR_DIG_PREFETCH_SUFFIX "dig_prefetch" > >> +#define XATTR_NAME_DIG_PREFETCH XATTR_SECURITY_PREFIX XATTR_DIG_PREFETCH_SUFFIX > >> + > >> #define XATTR_SELINUX_SUFFIX "selinux" > >> #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX > >> > >> diff --git a/security/digest_cache/dir.c b/security/digest_cache/dir.c > >> index 7bfcdd5f7ef1..a7d203c15386 100644 > >> --- a/security/digest_cache/dir.c > >> +++ b/security/digest_cache/dir.c > >> @@ -54,6 +54,7 @@ static bool digest_cache_dir_iter(struct dir_context *__ctx, const char *name, > >> new_entry->seq_num = UINT_MAX; > >> new_entry->digest_cache = NULL; > >> mutex_init(&new_entry->digest_cache_mutex); > >> + new_entry->prefetched = false; > >> > >> if (new_entry->name[0] < '0' || new_entry->name[0] > '9') > >> goto out; > >> @@ -127,6 +128,7 @@ int digest_cache_dir_create(struct digest_cache *digest_cache, > >> * @digest_cache: Digest cache > >> * @digest: Digest to search > >> * @algo: Algorithm of the digest to search > >> + * @filename: File name of the digest list to search > >> * > >> * This function iterates over the linked list created by > >> * digest_cache_dir_create() and looks up the digest in the digest cache of > >> @@ -149,7 +151,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > >> if (!dir_entry->digest_cache) { > >> cache = digest_cache_create(dentry, digest_list_path, > >> digest_cache->path_str, > >> - dir_entry->name); > >> + dir_entry->name, false, > >> + false); > >> /* Ignore digest caches that cannot be instantiated. */ > >> if (!cache) { > >> mutex_unlock(&dir_entry->digest_cache_mutex); > >> @@ -158,6 +161,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > >> > >> /* Consume extra ref. from digest_cache_create(). */ > >> dir_entry->digest_cache = cache; > >> + /* Digest list was read, mark entry as prefetched. */ > >> + dir_entry->prefetched = true; > >> } > >> mutex_unlock(&dir_entry->digest_cache_mutex); > >> > >> @@ -171,6 +176,54 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > >> return 0UL; > >> } > >> > >> +/** > >> + * digest_cache_dir_lookup_filename - Lookup a digest list > >> + * @dentry: Dentry of the file whose digest list is looked up > >> + * @digest_list_path: Path structure of the digest list directory > >> + * @digest_cache: Digest cache > >> + * @filename: File name of the digest list to search > >> + * > >> + * This function iterates over the linked list created by > >> + * digest_cache_dir_create() and looks up a digest list with a matching file > >> + * name among the entries. If there is no match, it prefetches (reads) the > >> + * current digest list. Otherwise, it returns the digest cache pointer from > >> + * digest_cache_create() to the caller. > >> + * > >> + * Return: A digest cache pointer if the digest list if found, NULL otherwise. > >> + */ > >> +struct digest_cache * > >> +digest_cache_dir_lookup_filename(struct dentry *dentry, > >> + struct path *digest_list_path, > >> + struct digest_cache *digest_cache, > >> + char *filename) > >> +{ > >> + struct digest_cache *cache; > >> + struct dir_entry *dir_entry; > >> + bool filename_found; > >> + > >> + list_for_each_entry(dir_entry, &digest_cache->dir_entries, list) { > >> + mutex_lock(&dir_entry->digest_cache_mutex); > >> + filename_found = !strcmp(dir_entry->name, filename); > >> + if (!filename_found && dir_entry->prefetched) { > >> + mutex_unlock(&dir_entry->digest_cache_mutex); > >> + continue; > >> + } > >> + > >> + cache = digest_cache_create(dentry, digest_list_path, > >> + digest_cache->path_str, > >> + dir_entry->name, false, > >> + filename_found ? false : true); > >> + > >> + dir_entry->prefetched = true; > >> + mutex_unlock(&dir_entry->digest_cache_mutex); > >> + > >> + if (filename_found) > >> + return cache; > >> + } > >> + > >> + return NULL; > >> +} > >> + > >> /** > >> * digest_cache_dir_free - Free the stored file list and put digest caches > >> * @digest_cache: Digest cache > >> diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h > >> index b7afca8e04da..c13b35f6b2c0 100644 > >> --- a/security/digest_cache/internal.h > >> +++ b/security/digest_cache/internal.h > >> @@ -17,6 +17,7 @@ > >> #define INIT_IN_PROGRESS 0 /* Digest cache being initialized. */ > >> #define INVALID 1 /* Digest cache marked as invalid. */ > >> #define IS_DIR 2 /* Digest cache created from dir. */ > >> +#define DIR_PREFETCH 3 /* Prefetching requested for dir. */ > >> > >> /** > >> * struct readdir_callback - Structure to store information for dir iteration > >> @@ -37,6 +38,7 @@ struct readdir_callback { > >> * @digest_cache: Digest cache associated to the directory entry > >> * @digest_cache_mutex: Protects @digest_cache > >> * @seq_num: Sequence number of the directory entry from file name > >> + * @prefetched: Whether the digest list has been already prefetched > >> * @name: File name of the directory entry > >> * > >> * This structure represents a directory entry with a digest cache created > >> @@ -47,6 +49,7 @@ struct dir_entry { > >> struct digest_cache *digest_cache; > >> struct mutex digest_cache_mutex; > >> unsigned int seq_num; > >> + bool prefetched; > >> char name[]; > >> } __packed; > >> > >> @@ -205,7 +208,8 @@ digest_cache_from_file_sec(const struct file *file) > >> /* main.c */ > >> struct digest_cache *digest_cache_create(struct dentry *dentry, > >> struct path *digest_list_path, > >> - char *path_str, char *filename); > >> + char *path_str, char *filename, > >> + bool prefetch_req, bool prefetch); > >> > >> /* htable.c */ > >> int digest_cache_htable_init(struct digest_cache *digest_cache, u64 num_digests, > >> @@ -236,6 +240,11 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, > >> struct path *digest_list_path, > >> struct digest_cache *digest_cache, u8 *digest, > >> enum hash_algo algo); > >> +struct digest_cache * > >> +digest_cache_dir_lookup_filename(struct dentry *dentry, > >> + struct path *digest_list_path, > >> + struct digest_cache *digest_cache, > >> + char *filename); > >> void digest_cache_dir_free(struct digest_cache *digest_cache); > >> > >> #endif /* _DIGEST_CACHE_INTERNAL_H */ > >> diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c > >> index 15f1486610a3..a5616fd07c1d 100644 > >> --- a/security/digest_cache/main.c > >> +++ b/security/digest_cache/main.c > >> @@ -83,6 +83,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) > >> * @digest_list_path: Path structure of the digest list > >> * @path_str: Path string of the digest list > >> * @filename: Digest list file name (can be an empty string) > >> + * @prefetch_req: Whether prefetching has been requested > >> + * @prefetch: Whether prefetching of a digest list is being done > >> * > >> * This function first locates, from the passed path, the digest list inode > >> * from which the digest cache will be created or retrieved (if it already > >> @@ -109,7 +111,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) > >> */ > >> struct digest_cache *digest_cache_create(struct dentry *dentry, > >> struct path *digest_list_path, > >> - char *path_str, char *filename) > >> + char *path_str, char *filename, > >> + bool prefetch_req, bool prefetch) > > > > > > This has enough parameters to consider separate "digest_cache_descriptor" > > or whatever. In some architectures this is beyond register parameters, > > which is IMHO good threshold to consider that. > > > > This will make e.g. tracing easier as you have to map only one parameter > > to a known struct to inspect the values. > > Uhm, seems still good (6 parameters). Sure, I can make a structure to > encapsulate the parameters, but will be used only for this purpose. Not > sure the code understandability will improve. I don't want to dictate this! So if you think it is best like this I'm cool too. So make your call and I won't come back to nag further :-) > > Thanks > > Roberto > > >> { > >> struct path file_path; > >> struct digest_cache *digest_cache = NULL; > >> @@ -148,6 +151,16 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > >> dentry->d_name.name); > >> goto out; > >> } > >> + > >> + if (prefetch) { > >> + /* Fine to fail, we are just prefetching. */ > >> + ret = digest_cache_populate(NULL, digest_list_path, > >> + path_str, filename); > >> + pr_debug("Digest list %s/%s %s prefetched\n", > >> + path_str, filename, > >> + !ret ? "has been" : "cannot be"); > >> + goto out; > >> + } > >> } > >> > >> dig_sec = digest_cache_get_security(inode); > >> @@ -176,6 +189,11 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > >> > >> /* Make the other lock contenders wait until creation complete. */ > >> set_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags); > >> + > >> + /* Set DIR_PREFETCH if prefetching was requested. */ > >> + if (prefetch_req) > >> + set_bit(DIR_PREFETCH, &digest_cache->flags); > >> + > >> mutex_unlock(&dig_sec->dig_owner_mutex); > >> > >> if (S_ISREG(inode->i_mode)) { > >> @@ -220,6 +238,52 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > >> return digest_cache; > >> } > >> > >> +/** > >> + * digest_cache_prefetch_requested - Verify if prefetching is requested > >> + * @digest_list_path: Path structure of the digest list directory > >> + * @path_str: Path string of the digest list directory > >> + * > >> + * This function verifies whether or not digest list prefetching is requested. > >> + * If dig_owner exists in the inode security blob, it checks the DIR_PREFETCH > >> + * bit (faster). Otherwise, it reads the new security.dig_prefetch xattr. > >> + * > >> + * Return: True if prefetching is requested, false otherwise. > >> + */ > >> +static bool digest_cache_prefetch_requested(struct path *digest_list_path, > >> + char *path_str) > >> +{ > >> + struct digest_cache_security *dig_sec; > >> + bool prefetch_req = false; > >> + char prefetch_value; > >> + struct inode *inode; > >> + int ret; > >> + > >> + inode = d_backing_inode(digest_list_path->dentry); > >> + dig_sec = digest_cache_get_security(inode); > >> + if (unlikely(!dig_sec)) > >> + return false; > >> + > >> + mutex_lock(&dig_sec->dig_owner_mutex); > >> + if (dig_sec->dig_owner) { > >> + /* Reliable test: DIR_PREFETCH set with dig_owner_mutex held. */ > >> + prefetch_req = test_bit(DIR_PREFETCH, > >> + &dig_sec->dig_owner->flags); > >> + mutex_unlock(&dig_sec->dig_owner_mutex); > >> + return prefetch_req; > >> + } > >> + mutex_unlock(&dig_sec->dig_owner_mutex); > >> + > >> + ret = vfs_getxattr(&nop_mnt_idmap, digest_list_path->dentry, > >> + XATTR_NAME_DIG_PREFETCH, &prefetch_value, 1); > >> + if (ret == 1 && prefetch_value == '1') { > >> + pr_debug("Prefetching has been enabled for directory %s\n", > >> + path_str); > >> + prefetch_req = true; > >> + } > >> + > >> + return prefetch_req; > >> +} > >> + > >> /** > >> * digest_cache_new - Retrieve digest list file name and request digest cache > >> * @dentry: Dentry of the inode for which the digest cache will be used > >> @@ -230,13 +294,19 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, > >> * with that file name. If security.digest_list is not found, this function > >> * requests the creation of a digest cache on the parent directory. > >> * > >> + * On prefetching, if the default path is a directory and if > >> + * security.digest_list is found, this function first retrieves the directory > >> + * digest cache, and then calls digest_cache_dir_lookup_filename() to retrieve > >> + * the desired digest cache in that directory. > >> + * > >> * Return: A new digest cache on success, NULL on error. > >> */ > >> static struct digest_cache *digest_cache_new(struct dentry *dentry) > >> { > >> char filename[NAME_MAX + 1] = { 0 }; > >> - struct digest_cache *digest_cache = NULL; > >> + struct digest_cache *digest_cache = NULL, *found; > >> struct path default_path; > >> + bool prefetch_req = false; > >> int ret; > >> > >> ret = kern_path(default_path_str, 0, &default_path); > >> @@ -273,9 +343,28 @@ static struct digest_cache *digest_cache_new(struct dentry *dentry) > >> pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n", > >> XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str, > >> filename); > >> + > >> + if (filename[0]) > >> + prefetch_req = digest_cache_prefetch_requested(&default_path, > >> + default_path_str); > >> create: > >> + /* On prefetching, retrieve the directory digest cache. */ > >> digest_cache = digest_cache_create(dentry, &default_path, > >> - default_path_str, filename); > >> + default_path_str, > >> + !prefetch_req ? filename : "", > >> + prefetch_req, false); > >> + if (!digest_cache) > >> + goto out; > >> + > >> + if (prefetch_req) { > >> + /* Find the digest cache with a matching file name. */ > >> + found = digest_cache_dir_lookup_filename(dentry, &default_path, > >> + digest_cache, > >> + filename); > >> + /* Release ref. to the directory digest cache. */ > >> + digest_cache_put(digest_cache); > >> + digest_cache = found; > >> + } > >> out: > >> path_put(&default_path); > >> return digest_cache; > >> diff --git a/security/digest_cache/populate.c b/security/digest_cache/populate.c > >> index 9c2fc2295310..17e7b011c367 100644 > >> --- a/security/digest_cache/populate.c > >> +++ b/security/digest_cache/populate.c > >> @@ -143,6 +143,12 @@ int digest_cache_populate(struct digest_cache *digest_cache, > >> return ret; > >> } > >> > >> + /* The caller wants just to read digest lists. */ > >> + if (!digest_cache) { > >> + ret = 0; > >> + goto out_vfree; > >> + } > >> + > >> data_len = digest_cache_strip_modsig(data, ret); > >> > >> /* Digest list parsers initialize the hash table and add the digests. */ > >> @@ -151,7 +157,7 @@ int digest_cache_populate(struct digest_cache *digest_cache, > >> if (ret < 0) > >> pr_debug("Error parsing digest list %s%s%s, ret: %d\n", > >> path_str, filename[0] ? "/" : "", filename, ret); > >> - > >> +out_vfree: > >> vfree(data); > >> return ret; > >> } > >> diff --git a/security/digest_cache/verif.c b/security/digest_cache/verif.c > >> index 04023240d3b4..c42ae93261e2 100644 > >> --- a/security/digest_cache/verif.c > >> +++ b/security/digest_cache/verif.c > >> @@ -33,7 +33,7 @@ static void free_verif(struct digest_cache_verif *verif) > >> * This function lets a verifier supply verification data about a digest list > >> * being read to populate the digest cache. > >> * > >> - * Return: Zero on success, -ENOMEM if out of memory. > >> + * Return: Zero on success, -ENOMEM if out of memory, -ENOENT on prefetching. > >> */ > >> int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, > >> size_t size) > >> @@ -41,6 +41,9 @@ int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, > >> struct digest_cache *digest_cache = digest_cache_from_file_sec(file); > >> struct digest_cache_verif *new_verif; > >> > >> + if (!digest_cache) > >> + return -ENOENT; > >> + > >> /* > >> * All allocations must be atomic (non-sleepable) since kprobe does not > >> * allow otherwise (kprobe is needed for testing). > > > > > > BR, Jarkko BR, Jarkko
diff --git a/include/uapi/linux/xattr.h b/include/uapi/linux/xattr.h index 8a58cf4bce65..8af33d38d9e8 100644 --- a/include/uapi/linux/xattr.h +++ b/include/uapi/linux/xattr.h @@ -57,6 +57,9 @@ #define XATTR_DIGEST_LIST_SUFFIX "digest_list" #define XATTR_NAME_DIGEST_LIST XATTR_SECURITY_PREFIX XATTR_DIGEST_LIST_SUFFIX +#define XATTR_DIG_PREFETCH_SUFFIX "dig_prefetch" +#define XATTR_NAME_DIG_PREFETCH XATTR_SECURITY_PREFIX XATTR_DIG_PREFETCH_SUFFIX + #define XATTR_SELINUX_SUFFIX "selinux" #define XATTR_NAME_SELINUX XATTR_SECURITY_PREFIX XATTR_SELINUX_SUFFIX diff --git a/security/digest_cache/dir.c b/security/digest_cache/dir.c index 7bfcdd5f7ef1..a7d203c15386 100644 --- a/security/digest_cache/dir.c +++ b/security/digest_cache/dir.c @@ -54,6 +54,7 @@ static bool digest_cache_dir_iter(struct dir_context *__ctx, const char *name, new_entry->seq_num = UINT_MAX; new_entry->digest_cache = NULL; mutex_init(&new_entry->digest_cache_mutex); + new_entry->prefetched = false; if (new_entry->name[0] < '0' || new_entry->name[0] > '9') goto out; @@ -127,6 +128,7 @@ int digest_cache_dir_create(struct digest_cache *digest_cache, * @digest_cache: Digest cache * @digest: Digest to search * @algo: Algorithm of the digest to search + * @filename: File name of the digest list to search * * This function iterates over the linked list created by * digest_cache_dir_create() and looks up the digest in the digest cache of @@ -149,7 +151,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, if (!dir_entry->digest_cache) { cache = digest_cache_create(dentry, digest_list_path, digest_cache->path_str, - dir_entry->name); + dir_entry->name, false, + false); /* Ignore digest caches that cannot be instantiated. */ if (!cache) { mutex_unlock(&dir_entry->digest_cache_mutex); @@ -158,6 +161,8 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, /* Consume extra ref. from digest_cache_create(). */ dir_entry->digest_cache = cache; + /* Digest list was read, mark entry as prefetched. */ + dir_entry->prefetched = true; } mutex_unlock(&dir_entry->digest_cache_mutex); @@ -171,6 +176,54 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, return 0UL; } +/** + * digest_cache_dir_lookup_filename - Lookup a digest list + * @dentry: Dentry of the file whose digest list is looked up + * @digest_list_path: Path structure of the digest list directory + * @digest_cache: Digest cache + * @filename: File name of the digest list to search + * + * This function iterates over the linked list created by + * digest_cache_dir_create() and looks up a digest list with a matching file + * name among the entries. If there is no match, it prefetches (reads) the + * current digest list. Otherwise, it returns the digest cache pointer from + * digest_cache_create() to the caller. + * + * Return: A digest cache pointer if the digest list if found, NULL otherwise. + */ +struct digest_cache * +digest_cache_dir_lookup_filename(struct dentry *dentry, + struct path *digest_list_path, + struct digest_cache *digest_cache, + char *filename) +{ + struct digest_cache *cache; + struct dir_entry *dir_entry; + bool filename_found; + + list_for_each_entry(dir_entry, &digest_cache->dir_entries, list) { + mutex_lock(&dir_entry->digest_cache_mutex); + filename_found = !strcmp(dir_entry->name, filename); + if (!filename_found && dir_entry->prefetched) { + mutex_unlock(&dir_entry->digest_cache_mutex); + continue; + } + + cache = digest_cache_create(dentry, digest_list_path, + digest_cache->path_str, + dir_entry->name, false, + filename_found ? false : true); + + dir_entry->prefetched = true; + mutex_unlock(&dir_entry->digest_cache_mutex); + + if (filename_found) + return cache; + } + + return NULL; +} + /** * digest_cache_dir_free - Free the stored file list and put digest caches * @digest_cache: Digest cache diff --git a/security/digest_cache/internal.h b/security/digest_cache/internal.h index b7afca8e04da..c13b35f6b2c0 100644 --- a/security/digest_cache/internal.h +++ b/security/digest_cache/internal.h @@ -17,6 +17,7 @@ #define INIT_IN_PROGRESS 0 /* Digest cache being initialized. */ #define INVALID 1 /* Digest cache marked as invalid. */ #define IS_DIR 2 /* Digest cache created from dir. */ +#define DIR_PREFETCH 3 /* Prefetching requested for dir. */ /** * struct readdir_callback - Structure to store information for dir iteration @@ -37,6 +38,7 @@ struct readdir_callback { * @digest_cache: Digest cache associated to the directory entry * @digest_cache_mutex: Protects @digest_cache * @seq_num: Sequence number of the directory entry from file name + * @prefetched: Whether the digest list has been already prefetched * @name: File name of the directory entry * * This structure represents a directory entry with a digest cache created @@ -47,6 +49,7 @@ struct dir_entry { struct digest_cache *digest_cache; struct mutex digest_cache_mutex; unsigned int seq_num; + bool prefetched; char name[]; } __packed; @@ -205,7 +208,8 @@ digest_cache_from_file_sec(const struct file *file) /* main.c */ struct digest_cache *digest_cache_create(struct dentry *dentry, struct path *digest_list_path, - char *path_str, char *filename); + char *path_str, char *filename, + bool prefetch_req, bool prefetch); /* htable.c */ int digest_cache_htable_init(struct digest_cache *digest_cache, u64 num_digests, @@ -236,6 +240,11 @@ digest_cache_dir_lookup_digest(struct dentry *dentry, struct path *digest_list_path, struct digest_cache *digest_cache, u8 *digest, enum hash_algo algo); +struct digest_cache * +digest_cache_dir_lookup_filename(struct dentry *dentry, + struct path *digest_list_path, + struct digest_cache *digest_cache, + char *filename); void digest_cache_dir_free(struct digest_cache *digest_cache); #endif /* _DIGEST_CACHE_INTERNAL_H */ diff --git a/security/digest_cache/main.c b/security/digest_cache/main.c index 15f1486610a3..a5616fd07c1d 100644 --- a/security/digest_cache/main.c +++ b/security/digest_cache/main.c @@ -83,6 +83,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) * @digest_list_path: Path structure of the digest list * @path_str: Path string of the digest list * @filename: Digest list file name (can be an empty string) + * @prefetch_req: Whether prefetching has been requested + * @prefetch: Whether prefetching of a digest list is being done * * This function first locates, from the passed path, the digest list inode * from which the digest cache will be created or retrieved (if it already @@ -109,7 +111,8 @@ static void digest_cache_free(struct digest_cache *digest_cache) */ struct digest_cache *digest_cache_create(struct dentry *dentry, struct path *digest_list_path, - char *path_str, char *filename) + char *path_str, char *filename, + bool prefetch_req, bool prefetch) { struct path file_path; struct digest_cache *digest_cache = NULL; @@ -148,6 +151,16 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, dentry->d_name.name); goto out; } + + if (prefetch) { + /* Fine to fail, we are just prefetching. */ + ret = digest_cache_populate(NULL, digest_list_path, + path_str, filename); + pr_debug("Digest list %s/%s %s prefetched\n", + path_str, filename, + !ret ? "has been" : "cannot be"); + goto out; + } } dig_sec = digest_cache_get_security(inode); @@ -176,6 +189,11 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, /* Make the other lock contenders wait until creation complete. */ set_bit(INIT_IN_PROGRESS, &dig_sec->dig_owner->flags); + + /* Set DIR_PREFETCH if prefetching was requested. */ + if (prefetch_req) + set_bit(DIR_PREFETCH, &digest_cache->flags); + mutex_unlock(&dig_sec->dig_owner_mutex); if (S_ISREG(inode->i_mode)) { @@ -220,6 +238,52 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, return digest_cache; } +/** + * digest_cache_prefetch_requested - Verify if prefetching is requested + * @digest_list_path: Path structure of the digest list directory + * @path_str: Path string of the digest list directory + * + * This function verifies whether or not digest list prefetching is requested. + * If dig_owner exists in the inode security blob, it checks the DIR_PREFETCH + * bit (faster). Otherwise, it reads the new security.dig_prefetch xattr. + * + * Return: True if prefetching is requested, false otherwise. + */ +static bool digest_cache_prefetch_requested(struct path *digest_list_path, + char *path_str) +{ + struct digest_cache_security *dig_sec; + bool prefetch_req = false; + char prefetch_value; + struct inode *inode; + int ret; + + inode = d_backing_inode(digest_list_path->dentry); + dig_sec = digest_cache_get_security(inode); + if (unlikely(!dig_sec)) + return false; + + mutex_lock(&dig_sec->dig_owner_mutex); + if (dig_sec->dig_owner) { + /* Reliable test: DIR_PREFETCH set with dig_owner_mutex held. */ + prefetch_req = test_bit(DIR_PREFETCH, + &dig_sec->dig_owner->flags); + mutex_unlock(&dig_sec->dig_owner_mutex); + return prefetch_req; + } + mutex_unlock(&dig_sec->dig_owner_mutex); + + ret = vfs_getxattr(&nop_mnt_idmap, digest_list_path->dentry, + XATTR_NAME_DIG_PREFETCH, &prefetch_value, 1); + if (ret == 1 && prefetch_value == '1') { + pr_debug("Prefetching has been enabled for directory %s\n", + path_str); + prefetch_req = true; + } + + return prefetch_req; +} + /** * digest_cache_new - Retrieve digest list file name and request digest cache * @dentry: Dentry of the inode for which the digest cache will be used @@ -230,13 +294,19 @@ struct digest_cache *digest_cache_create(struct dentry *dentry, * with that file name. If security.digest_list is not found, this function * requests the creation of a digest cache on the parent directory. * + * On prefetching, if the default path is a directory and if + * security.digest_list is found, this function first retrieves the directory + * digest cache, and then calls digest_cache_dir_lookup_filename() to retrieve + * the desired digest cache in that directory. + * * Return: A new digest cache on success, NULL on error. */ static struct digest_cache *digest_cache_new(struct dentry *dentry) { char filename[NAME_MAX + 1] = { 0 }; - struct digest_cache *digest_cache = NULL; + struct digest_cache *digest_cache = NULL, *found; struct path default_path; + bool prefetch_req = false; int ret; ret = kern_path(default_path_str, 0, &default_path); @@ -273,9 +343,28 @@ static struct digest_cache *digest_cache_new(struct dentry *dentry) pr_debug("Found %s xattr in %s, default path: %s, digest list: %s\n", XATTR_NAME_DIGEST_LIST, dentry->d_name.name, default_path_str, filename); + + if (filename[0]) + prefetch_req = digest_cache_prefetch_requested(&default_path, + default_path_str); create: + /* On prefetching, retrieve the directory digest cache. */ digest_cache = digest_cache_create(dentry, &default_path, - default_path_str, filename); + default_path_str, + !prefetch_req ? filename : "", + prefetch_req, false); + if (!digest_cache) + goto out; + + if (prefetch_req) { + /* Find the digest cache with a matching file name. */ + found = digest_cache_dir_lookup_filename(dentry, &default_path, + digest_cache, + filename); + /* Release ref. to the directory digest cache. */ + digest_cache_put(digest_cache); + digest_cache = found; + } out: path_put(&default_path); return digest_cache; diff --git a/security/digest_cache/populate.c b/security/digest_cache/populate.c index 9c2fc2295310..17e7b011c367 100644 --- a/security/digest_cache/populate.c +++ b/security/digest_cache/populate.c @@ -143,6 +143,12 @@ int digest_cache_populate(struct digest_cache *digest_cache, return ret; } + /* The caller wants just to read digest lists. */ + if (!digest_cache) { + ret = 0; + goto out_vfree; + } + data_len = digest_cache_strip_modsig(data, ret); /* Digest list parsers initialize the hash table and add the digests. */ @@ -151,7 +157,7 @@ int digest_cache_populate(struct digest_cache *digest_cache, if (ret < 0) pr_debug("Error parsing digest list %s%s%s, ret: %d\n", path_str, filename[0] ? "/" : "", filename, ret); - +out_vfree: vfree(data); return ret; } diff --git a/security/digest_cache/verif.c b/security/digest_cache/verif.c index 04023240d3b4..c42ae93261e2 100644 --- a/security/digest_cache/verif.c +++ b/security/digest_cache/verif.c @@ -33,7 +33,7 @@ static void free_verif(struct digest_cache_verif *verif) * This function lets a verifier supply verification data about a digest list * being read to populate the digest cache. * - * Return: Zero on success, -ENOMEM if out of memory. + * Return: Zero on success, -ENOMEM if out of memory, -ENOENT on prefetching. */ int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, size_t size) @@ -41,6 +41,9 @@ int digest_cache_verif_set(struct file *file, const char *verif_id, void *data, struct digest_cache *digest_cache = digest_cache_from_file_sec(file); struct digest_cache_verif *new_verif; + if (!digest_cache) + return -ENOENT; + /* * All allocations must be atomic (non-sleepable) since kprobe does not * allow otherwise (kprobe is needed for testing).