From: Eric Biggers ebiggers@google.com
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 Signed-off-by: Eric Biggers ebiggers@google.com --- fs/verity/signature.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-)
diff --git a/fs/verity/signature.c b/fs/verity/signature.c index b95acae64eac6..f6668d92d8151 100644 --- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -70,10 +70,26 @@ int fsverity_verify_signature(const struct fsverity_info *vi, d->digest_size = cpu_to_le16(hash_alg->digest_size); memcpy(d->digest, vi->file_digest, hash_alg->digest_size);
- err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, - signature, sig_size, fsverity_keyring, - VERIFYING_UNSPECIFIED_SIGNATURE, - NULL, NULL); + 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. + */ + err = -ENOKEY; + } else { + err = verify_pkcs7_signature(d, + sizeof(*d) + hash_alg->digest_size, + signature, sig_size, + fsverity_keyring, + VERIFYING_UNSPECIFIED_SIGNATURE, + NULL, NULL); + } kfree(d);
if (err) {
base-commit: 456ae5fe9b448f44ebe98b391a3bae9c75df465e