Re: [PATCH] fsverity: skip PKCS#7 parser when keyring is empty

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Should the whole use of "d" be moved into the else block?


On Mon, Jul 31, 2023 at 10:09 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
>  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
> --
> 2.41.0
>




[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux