[bpf-next,v3,1/3] ima: Implement ima_inode_hash

Commit Message

KP Singh Nov. 24, 2020, 3:12 p.m. UTC

From: KP Singh <[e-mail]>

This is in preparation to add a helper for BPF LSM programs to use
IMA hashes when attached to LSM hooks. There are LSM hooks like
inode_unlink which do not have a struct file * argument and cannot
use the existing ima_file_hash API.

An inode based API is, therefore, useful in LSM based detections like an
executable trying to delete itself which rely on the inode_unlink LSM
hook.

Moreover, the ima_file_hash function does nothing with the struct file
pointer apart from calling file_inode on it and converting it to an
inode.

Signed-off-by: KP Singh <[e-mail]>
---
 include/linux/ima.h               |  6 +++
 security/integrity/ima/ima_main.c | 78 +++++++++++++++++++++----------
 2 files changed, 60 insertions(+), 24 deletions(-)

Comments

Yonghong Song Nov. 24, 2020, 5:35 p.m. UTC | #1

On 11/24/20 7:12 AM, KP Singh wrote:
> From: KP Singh <[e-mail]>
> 
> This is in preparation to add a helper for BPF LSM programs to use
> IMA hashes when attached to LSM hooks. There are LSM hooks like
> inode_unlink which do not have a struct file * argument and cannot
> use the existing ima_file_hash API.
> 
> An inode based API is, therefore, useful in LSM based detections like an
> executable trying to delete itself which rely on the inode_unlink LSM
> hook.
> 
> Moreover, the ima_file_hash function does nothing with the struct file
> pointer apart from calling file_inode on it and converting it to an
> inode.
> 
> Signed-off-by: KP Singh <[e-mail]>

There is no change for this patch compared to previous version,
so you can carry my Ack.

Acked-by: Yonghong Song <[e-mail]>

KP Singh Nov. 25, 2020, 12:04 p.m. UTC | #2

On Tue, Nov 24, 2020 at 6:35 PM Yonghong Song <[e-mail]> wrote:
>
>
>
> On 11/24/20 7:12 AM, KP Singh wrote:
> > From: KP Singh <[e-mail]>
> >
> > This is in preparation to add a helper for BPF LSM programs to use
> > IMA hashes when attached to LSM hooks. There are LSM hooks like
> > inode_unlink which do not have a struct file * argument and cannot
> > use the existing ima_file_hash API.
> >
> > An inode based API is, therefore, useful in LSM based detections like an
> > executable trying to delete itself which rely on the inode_unlink LSM
> > hook.
> >
> > Moreover, the ima_file_hash function does nothing with the struct file
> > pointer apart from calling file_inode on it and converting it to an
> > inode.
> >
> > Signed-off-by: KP Singh <[e-mail]>
>
> There is no change for this patch compared to previous version,
> so you can carry my Ack.
>
> Acked-by: Yonghong Song <[e-mail]>

I am guessing:

*  We need an Ack from Mimi/James.
* As regards to which tree, I guess bpf-next would be better since the
BPF helper and the selftest depends on it

Daniel Borkmann Nov. 25, 2020, 12:17 p.m. UTC | #3

On 11/25/20 1:04 PM, KP Singh wrote:
> On Tue, Nov 24, 2020 at 6:35 PM Yonghong Song <[e-mail]> wrote:
>> On 11/24/20 7:12 AM, KP Singh wrote:
>>> From: KP Singh <[e-mail]>
>>>
>>> This is in preparation to add a helper for BPF LSM programs to use
>>> IMA hashes when attached to LSM hooks. There are LSM hooks like
>>> inode_unlink which do not have a struct file * argument and cannot
>>> use the existing ima_file_hash API.
>>>
>>> An inode based API is, therefore, useful in LSM based detections like an
>>> executable trying to delete itself which rely on the inode_unlink LSM
>>> hook.
>>>
>>> Moreover, the ima_file_hash function does nothing with the struct file
>>> pointer apart from calling file_inode on it and converting it to an
>>> inode.
>>>
>>> Signed-off-by: KP Singh <[e-mail]>
>>
>> There is no change for this patch compared to previous version,
>> so you can carry my Ack.
>>
>> Acked-by: Yonghong Song <[e-mail]>
> 
> I am guessing:
> 
> *  We need an Ack from Mimi/James.

Yes.

> * As regards to which tree, I guess bpf-next would be better since the
> BPF helper and the selftest depends on it

Yep, bpf-next is my preference as otherwise we're running into unnecessary
merge conflicts.

Thanks,
Daniel

Mimi Zohar Nov. 25, 2020, 12:27 p.m. UTC | #4

On Tue, 2020-11-24 at 15:12 +0000, KP Singh wrote:
> From: KP Singh <[e-mail]>
> 
> This is in preparation to add a helper for BPF LSM programs to use
> IMA hashes when attached to LSM hooks. There are LSM hooks like
> inode_unlink which do not have a struct file * argument and cannot
> use the existing ima_file_hash API.
> 
> An inode based API is, therefore, useful in LSM based detections like an
> executable trying to delete itself which rely on the inode_unlink LSM
> hook.
> 
> Moreover, the ima_file_hash function does nothing with the struct file
> pointer apart from calling file_inode on it and converting it to an
> inode.
> 
> Signed-off-by: KP Singh <[e-mail]>


Acked-by: Mimi Zohar <[e-mail]>

Patch

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 8fa7bcfb2da2..7233a2751754 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -29,6 +29,7 @@  extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
 extern void ima_post_path_mknod(struct dentry *dentry);
 extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
+extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);
 extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
 
 #ifdef CONFIG_IMA_KEXEC
@@ -115,6 +116,11 @@  static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size)
 	return -EOPNOTSUPP;
 }
 
+static inline int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}
 #endif /* CONFIG_IMA */
 
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 2d1af8899cab..cb2deaa188e7 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -501,37 +501,14 @@  int ima_file_check(struct file *file, int mask)
 }
 EXPORT_SYMBOL_GPL(ima_file_check);
 
-/**
- * ima_file_hash - return the stored measurement if a file has been hashed and
- * is in the iint cache.
- * @file: pointer to the file
- * @buf: buffer in which to store the hash
- * @buf_size: length of the buffer
- *
- * On success, return the hash algorithm (as defined in the enum hash_algo).
- * If buf is not NULL, this function also outputs the hash into buf.
- * If the hash is larger than buf_size, then only buf_size bytes will be copied.
- * It generally just makes sense to pass a buffer capable of holding the largest
- * possible hash: IMA_MAX_DIGEST_SIZE.
- * The file hash returned is based on the entire file, including the appended
- * signature.
- *
- * If IMA is disabled or if no measurement is available, return -EOPNOTSUPP.
- * If the parameters are incorrect, return -EINVAL.
- */
-int ima_file_hash(struct file *file, char *buf, size_t buf_size)
+static int __ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
 {
-	struct inode *inode;
 	struct integrity_iint_cache *iint;
 	int hash_algo;
 
-	if (!file)
-		return -EINVAL;
-
 	if (!ima_policy_flag)
 		return -EOPNOTSUPP;
 
-	inode = file_inode(file);
 	iint = integrity_iint_find(inode);
 	if (!iint)
 		return -EOPNOTSUPP;
@@ -558,8 +535,61 @@  int ima_file_hash(struct file *file, char *buf, size_t buf_size)
 
 	return hash_algo;
 }
+
+/**
+ * ima_file_hash - return the stored measurement if a file has been hashed and
+ * is in the iint cache.
+ * @file: pointer to the file
+ * @buf: buffer in which to store the hash
+ * @buf_size: length of the buffer
+ *
+ * On success, return the hash algorithm (as defined in the enum hash_algo).
+ * If buf is not NULL, this function also outputs the hash into buf.
+ * If the hash is larger than buf_size, then only buf_size bytes will be copied.
+ * It generally just makes sense to pass a buffer capable of holding the largest
+ * possible hash: IMA_MAX_DIGEST_SIZE.
+ * The file hash returned is based on the entire file, including the appended
+ * signature.
+ *
+ * If IMA is disabled or if no measurement is available, return -EOPNOTSUPP.
+ * If the parameters are incorrect, return -EINVAL.
+ */
+int ima_file_hash(struct file *file, char *buf, size_t buf_size)
+{
+	if (!file)
+		return -EINVAL;
+
+	return __ima_inode_hash(file_inode(file), buf, buf_size);
+}
 EXPORT_SYMBOL_GPL(ima_file_hash);
 
+/**
+ * ima_inode_hash - return the stored measurement if the inode has been hashed
+ * and is in the iint cache.
+ * @inode: pointer to the inode
+ * @buf: buffer in which to store the hash
+ * @buf_size: length of the buffer
+ *
+ * On success, return the hash algorithm (as defined in the enum hash_algo).
+ * If buf is not NULL, this function also outputs the hash into buf.
+ * If the hash is larger than buf_size, then only buf_size bytes will be copied.
+ * It generally just makes sense to pass a buffer capable of holding the largest
+ * possible hash: IMA_MAX_DIGEST_SIZE.
+ * The hash returned is based on the entire contents, including the appended
+ * signature.
+ *
+ * If IMA is disabled or if no measurement is available, return -EOPNOTSUPP.
+ * If the parameters are incorrect, return -EINVAL.
+ */
+int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size)
+{
+	if (!inode)
+		return -EINVAL;
+
+	return __ima_inode_hash(inode, buf, buf_size);
+}
+EXPORT_SYMBOL_GPL(ima_inode_hash);
+
 /**
  * ima_post_create_tmpfile - mark newly created tmpfile as new
  * @file : newly created tmpfile