Messages in this thread | | | Subject | Re: [PATCH v2] ima: Fix NULL pointer dereference in ima_file_hash | From | Mimi Zohar <> | Date | Wed, 16 Sep 2020 12:00:10 -0400 |
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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; >
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