| Message ID | 20200916124931.1254990-1-kpsingh@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] ima: Fix NULL pointer dereference in ima_file_hash | expand |
On Wed, Sep 16, 2020 at 2:49 PM KP Singh <kpsingh@chromium.org> wrote: > > From: KP Singh <kpsingh@google.com> [...] Another attempt to get this on the lists. > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > index 8a91711ca79b..4c86cd4eece0 100644 > --- a/security/integrity/ima/ima_main.c > +++ b/security/integrity/ima/ima_main.c > @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size) > return -EOPNOTSUPP; > > mutex_lock(&iint->mutex); > + > + /* > + * ima_file_hash can be called when ima_collect_measurement has still > + * not been called, we might not always have a hash. > + */ > + if (!iint->ima_hash) { > + mutex_unlock(&iint->mutex); > + return -EOPNOTSUPP; > + } > + > if (buf) { > size_t copied_size; > > -- > 2.28.0.526.ge36021eeef-goog >
On Wed, 2020-09-16 at 14:49 +0200, KP Singh wrote: > From: KP Singh <kpsingh@google.com> > > ima_file_hash can be called when there is no iint->ima_hash available > even though the inode exists in the integrity cache. > > An example where this can happen (suggested by Jann Horn): > > Process A does: > > while(1) { > unlink("/tmp/imafoo"); > fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700); > if (fd == -1) { > perror("open"); > continue; > } > write(fd, "A", 1); > close(fd); > } > > and Process B does: > > while (1) { > int fd = open("/tmp/imafoo", O_RDONLY); > if (fd == -1) > continue; > char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC, > MAP_PRIVATE, fd, 0); > if (mapping != MAP_FAILED) > munmap(mapping, 0x1000); > close(fd); > } > > Due to the race to get the iint->mutex between ima_file_hash and > process_measurement iint->ima_hash could still be NULL. > > Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash of a given file") > Signed-off-by: KP Singh <kpsingh@google.com> > Reviewed-by: Florent Revest <revest@chromium.org> > --- > security/integrity/ima/ima_main.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > index 8a91711ca79b..4c86cd4eece0 100644 > --- a/security/integrity/ima/ima_main.c > +++ b/security/integrity/ima/ima_main.c > @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size) > return -EOPNOTSUPP; > > mutex_lock(&iint->mutex); > + > + /* > + * ima_file_hash can be called when ima_collect_measurement has still > + * not been called, we might not always have a hash. > + */ > + if (!iint->ima_hash) { > + mutex_unlock(&iint->mutex); > + return -EOPNOTSUPP; > + } > + Not having a file hash is rather common (e.g. mknodat, prior to the file being closed). Before appraising the integrity of a file, it checks whether it is a new file (eg. IMA_NEW_FILE), but, unfortunately, the flag is only set for those files in the appraise policy. The patch looks fine, but you might want to reflect not having a file hash is common in the patch description. Mimi > if (buf) { > size_t copied_size; >
On Wed, Sep 16, 2020 at 6:00 PM Mimi Zohar <zohar@linux.ibm.com> wrote: > > On Wed, 2020-09-16 at 14:49 +0200, KP Singh wrote: > > From: KP Singh <kpsingh@google.com> > > > > ima_file_hash can be called when there is no iint->ima_hash available > > even though the inode exists in the integrity cache. > > > > An example where this can happen (suggested by Jann Horn): > > > > Process A does: > > > > while(1) { > > unlink("/tmp/imafoo"); > > fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700); > > if (fd == -1) { > > perror("open"); > > continue; > > } > > write(fd, "A", 1); > > close(fd); > > } > > > > and Process B does: > > > > while (1) { > > int fd = open("/tmp/imafoo", O_RDONLY); > > if (fd == -1) > > continue; > > char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC, > > MAP_PRIVATE, fd, 0); > > if (mapping != MAP_FAILED) > > munmap(mapping, 0x1000); > > close(fd); > > } > > > > Due to the race to get the iint->mutex between ima_file_hash and > > process_measurement iint->ima_hash could still be NULL. > > > > Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash of a given file") > > Signed-off-by: KP Singh <kpsingh@google.com> > > Reviewed-by: Florent Revest <revest@chromium.org> > > --- > > security/integrity/ima/ima_main.c | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > > index 8a91711ca79b..4c86cd4eece0 100644 > > --- a/security/integrity/ima/ima_main.c > > +++ b/security/integrity/ima/ima_main.c > > @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size) > > return -EOPNOTSUPP; > > > > mutex_lock(&iint->mutex); > > + > > + /* > > + * ima_file_hash can be called when ima_collect_measurement has still > > + * not been called, we might not always have a hash. > > + */ > > + if (!iint->ima_hash) { > > + mutex_unlock(&iint->mutex); > > + return -EOPNOTSUPP; > > + } > > + > > Not having a file hash is rather common (e.g. mknodat, prior to the > file being closed). Before appraising the integrity of a file, it > checks whether it is a new file (eg. IMA_NEW_FILE), but, unfortunately, > the flag is only set for those files in the appraise policy. Makes sense. > > The patch looks fine, but you might want to reflect not having a file > hash is common in the patch description. > Thanks! Will send another revision with an updated description. - KP > Mimi > > > if (buf) { > > size_t copied_size; > > > >
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index 8a91711ca79b..4c86cd4eece0 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size) return -EOPNOTSUPP; mutex_lock(&iint->mutex); + + /* + * ima_file_hash can be called when ima_collect_measurement has still + * not been called, we might not always have a hash. + */ + if (!iint->ima_hash) { + mutex_unlock(&iint->mutex); + return -EOPNOTSUPP; + } + if (buf) { size_t copied_size;