On Wed, 2022-02-23 at 17:26 -0800, Eric Biggers wrote:
> On Wed, Feb 23, 2022 at 08:21:01PM -0500, Mimi Zohar wrote:
> > On Wed, 2022-02-23 at 15:59 -0800, Eric Biggers wrote:
> > > On Fri, Feb 11, 2022 at 04:43:05PM -0500, Mimi Zohar wrote:
> > > > +/**
> > > > + * fsverity_get_digest() - get a verity file's digest
> > > > + * @inode: inode to get digest of
> > > > + * @digest: (out) pointer to the digest
> > > > + * @alg: (out) pointer to the hash algorithm enumeration
> > > > + *
> > > > + * Return the file hash algorithm and digest of an fsverity protected file.
> > > > + *
> > > > + * Return: 0 on success, -errno on failure
> > > > + */
> > > > +int fsverity_get_digest(struct inode *inode,
> > > > + u8 digest[FS_VERITY_MAX_DIGEST_SIZE],
> > > > + enum hash_algo *alg)
> > > > +{
> > > > + const struct fsverity_info *vi;
> > > > + const struct fsverity_hash_alg *hash_alg;
> > > > + int i;
> > > > +
> > > > + vi = fsverity_get_info(inode);
> > > > + if (!vi)
> > > > + return -ENODATA; /* not a verity file */
> > >
> > > Sorry for the slow reviews; I'm taking a look again now. One question about
> > > something I missed earlier: is the file guaranteed to have been opened before
> > > this is called? fsverity_get_info() only returns a non-NULL value if the file
> > > has been opened at least once since the inode has been loaded into memory. If
> > > the inode has just been loaded into memory without being opened, for example due
> > > to a call to stat(), then fsverity_get_info() will return NULL.
> > >
> > > If the file is guaranteed to have been opened, then the code is fine, but the
> > > comment for fsverity_get_digest() perhaps should be updated to mention this
> > > assumption, given that it takes a struct inode rather than a struct file.
> > >
> > > If the file is *not* guaranteed to have been opened, then it would be necessary
> > > to make fsverity_get_digest() call ensure_verity_info() to set up the
> > > fsverity_info.
> >
> > Yes, fsverity_get_digest() is called as a result of a syscall - open,
> > execve, mmap, etc.
> > Refer to the LSM hooks security_bprm_check() and security_mmap_file().
> > ima_file_check() is called directly in do_open().
>
> stat() is a syscall too, so the question is not whether this is being called as
> a result of a syscall, but rather whether it's only being called while the file
> is open (or at least previously opened). Is the answer to that "yes"?
yes
