fs-verity: don't pass whole descriptor to fsverity_verify_signature()

Now that fsverity_get_descriptor() validates the sig_size field,
fsverity_verify_signature() doesn't need to do it.

Just change the prototype of fsverity_verify_signature() to take the
signature directly rather than take a fsverity_descriptor.

Link: https://lore.kernel.org/r/20210115181819.34732-3-ebiggers@kernel.orgReviewed-by: Victor Hsieh <victorhsieh@google.com>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Reviewed-by: Amy Parker <enbyamy@gmail.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/verity/fsverity_private.h

@@ -140,15 +140,13 @@ void __init fsverity_exit_info_cache(void);
 
 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
 int fsverity_verify_signature(const struct fsverity_info *vi,
-			      const struct fsverity_descriptor *desc,
-			      size_t desc_size);
+			      const u8 *signature, size_t sig_size);
 
 int __init fsverity_init_signature(void);
 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
 static inline int
 fsverity_verify_signature(const struct fsverity_info *vi,
-			  const struct fsverity_descriptor *desc,
-			  size_t desc_size)
+			  const u8 *signature, size_t sig_size)
 {
 	return 0;
 }

fs/verity/open.c

@@ -181,7 +181,8 @@ struct fsverity_info *fsverity_create_info(const struct inode *inode,
 		 vi->tree_params.hash_alg->name,
 		 vi->tree_params.digest_size, vi->file_digest);
 
-	err = fsverity_verify_signature(vi, desc, desc_size);
+	err = fsverity_verify_signature(vi, desc->signature,
+					le32_to_cpu(desc->sig_size));
 out:
 	if (err) {
 		fsverity_free_info(vi);

fs/verity/signature.c

@@ -29,21 +29,19 @@ static struct key *fsverity_keyring;
 /**
  * fsverity_verify_signature() - check a verity file's signature
  * @vi: the file's fsverity_info
- * @desc: the file's fsverity_descriptor
- * @desc_size: size of @desc
+ * @signature: the file's built-in signature
+ * @sig_size: size of signature in bytes, or 0 if no signature
  *
- * If the file's fs-verity descriptor includes a signature of the file digest,
- * verify it against the certificates in the fs-verity keyring.
+ * If the file includes a signature of its fs-verity file digest, verify it
+ * against the certificates in the fs-verity keyring.
  *
  * Return: 0 on success (signature valid or not required); -errno on failure
  */
 int fsverity_verify_signature(const struct fsverity_info *vi,
-			      const struct fsverity_descriptor *desc,
-			      size_t desc_size)
+			      const u8 *signature, size_t sig_size)
 {
 	const struct inode *inode = vi->inode;
 	const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg;
-	const u32 sig_size = le32_to_cpu(desc->sig_size);
 	struct fsverity_formatted_digest *d;
 	int err;
 
@@ -56,11 +54,6 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
 		return 0;
 	}
 
-	if (sig_size > desc_size - sizeof(*desc)) {
-		fsverity_err(inode, "Signature overflows verity descriptor");
-		return -EBADMSG;
-	}
-
 	d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
 	if (!d)
 		return -ENOMEM;
@@ -70,8 +63,7 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
 	memcpy(d->digest, vi->file_digest, hash_alg->digest_size);
 
 	err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
-				     desc->signature, sig_size,
-				     fsverity_keyring,
+				     signature, sig_size, fsverity_keyring,
 				     VERIFYING_UNSPECIFIED_SIGNATURE,
 				     NULL, NULL);
 	kfree(d);