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: [email protected]
Reviewed-by: Jarkko Sakkinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Eric Biggers <[email protected]>

0 files changed, 0 insertions, 0 deletions