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SubjectRe: [PATCH v7 1/5] fs-verity: define a function to return the integrity protected file digest
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Hi Scott,

On Mon, 2022-03-28 at 11:45 +0800, Guozihua (Scott) 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.
> > + * Assumption: before calling fsverity_get_digest(), the file must have been
> > + * opened.
> > + *
> > + * 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 */
> > +
> > + hash_alg = vi->tree_params.hash_alg;
> > + memset(digest, 0, FS_VERITY_MAX_DIGEST_SIZE);
>
> Hi Mimi,
>
> I would suggest moving this memset downward right before the memcpy.

By doing it here, any existing garbage stored in the digest is cleared
before returning a failure.

thanks,

Mimi
>
> > +
> > + /* convert the verity hash algorithm name to a hash_algo_name enum */
> > + i = match_string(hash_algo_name, HASH_ALGO__LAST, hash_alg->name);
> > + if (i < 0)
> > + return -EINVAL;
> > + *alg = i;
> > +
> > + if (WARN_ON_ONCE(hash_alg->digest_size != hash_digest_size[*alg]))
> > + return -EINVAL;
> > + memcpy(digest, vi->file_digest, hash_alg->digest_size);
> > +
> > + pr_debug("file digest %s:%*phN\n", hash_algo_name[*alg],
> > + hash_digest_size[*alg], digest);
> > +
> > + return 0;


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