6.4-stable review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit 919dc320956ea353a7fb2d84265195ad5ef525ac upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/verity/signature.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
--- a/fs/verity/signature.c +++ b/fs/verity/signature.c @@ -54,6 +54,22 @@ int fsverity_verify_signature(const stru 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;