summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorEric Biggers <ebiggers@google.com>2023-08-01 21:03:53 -0700
committerEric Biggers <ebiggers@google.com>2023-08-20 10:33:43 -0700
commit919dc320956ea353a7fb2d84265195ad5ef525ac (patch)
treea57aa31c1764f05b43a8165f664f4c30dda6e7ff
parent456ae5fe9b448f44ebe98b391a3bae9c75df465e (diff)
downloadlinux-919dc320956ea353a7fb2d84265195ad5ef525ac.tar.gz
linux-919dc320956ea353a7fb2d84265195ad5ef525ac.tar.bz2
linux-919dc320956ea353a7fb2d84265195ad5ef525ac.zip
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>
-rw-r--r--fs/verity/signature.c16
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;