diff options
| author | Eric Biggers <ebiggers@google.com> | 2023-08-01 21:03:53 -0700 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2023-08-20 10:33:43 -0700 |
| commit | 919dc320956ea353a7fb2d84265195ad5ef525ac (patch) | |
| tree | a57aa31c1764f05b43a8165f664f4c30dda6e7ff /fs/verity | |
| parent | 456ae5fe9b448f44ebe98b391a3bae9c75df465e (diff) | |
fsverity: skip PKCS#7 parser when keyring is empty
If an fsverity builtin signature is given for a file but the
".fs-verity" keyring is empty, there's no real reason to run the PKCS#7
parser. Skip this to avoid the PKCS#7 attack surface when builtin
signature support is configured into the kernel but is not being used.
This is a hardening improvement, not a fix per se, but I've added
Fixes and Cc stable to get it out to more users.
Fixes: 432434c9f8e1 ("fs-verity: support builtin file signatures")
Cc: stable@vger.kernel.org
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/r/20230820173237.2579-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/verity')
| -rw-r--r-- | fs/verity/signature.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/fs/verity/signature.c b/fs/verity/signature.c index b95acae64eac..90c07573dd77 100644 --- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -62,6 +62,22 @@ int fsverity_verify_signature(const struct fsverity_info *vi, return 0; } + if (fsverity_keyring->keys.nr_leaves_on_tree == 0) { + /* + * The ".fs-verity" keyring is empty, due to builtin signatures + * being supported by the kernel but not actually being used. + * In this case, verify_pkcs7_signature() would always return an + * error, usually ENOKEY. It could also be EBADMSG if the + * PKCS#7 is malformed, but that isn't very important to + * distinguish. So, just skip to ENOKEY to avoid the attack + * surface of the PKCS#7 parser, which would otherwise be + * reachable by any task able to execute FS_IOC_ENABLE_VERITY. + */ + fsverity_err(inode, + "fs-verity keyring is empty, rejecting signed file!"); + return -ENOKEY; + } + d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); if (!d) return -ENOMEM; |