Re: [PATCH v4 1/3] KEYS: Introduce keyring_is_empty()

[Ignat Korchagin]

On Thu, Oct 29, 2026 at 11:25 PM Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote:
>
> Introduce keyring_is_empty() in order to decouple for BPF, dm-verity and
> fs-verity how keyring internally manages the keys.
>
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

Reviewed-by: Ignat Korchagin <ignat@xxxxxxxxx>

> ---
>  drivers/md/dm-verity-verify-sig.c                      |  2 +-
>  fs/verity/signature.c                                  |  2 +-
>  include/linux/key.h                                    |  1 +
>  kernel/bpf/keys.c                                      |  2 +-
>  security/keys/keyring.c                                | 10 ++++++++++
>  .../selftests/dm-verity/test-dm-verity-keyring.sh      |  2 +-
>  6 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c
> index aadcf5e4a47c..cad21e9144ed 100644
> --- a/drivers/md/dm-verity-verify-sig.c
> +++ b/drivers/md/dm-verity-verify-sig.c
> @@ -153,7 +153,7 @@ int verity_verify_root_hash(const void *root_hash, size_t root_hash_len,
>         if (ret != -ENOKEY && ret != -EKEYREJECTED)
>                 return ret;
>
> -       if (dm_verity_keyring->keys.nr_leaves_on_tree &&
> +       if (!keyring_is_empty(dm_verity_keyring) &&
>             dm_verity_keyring->restrict_link)
>                 ret = verify_pkcs7_signature(root_hash, root_hash_len,
>                                              sig_data, sig_len,
> diff --git a/fs/verity/signature.c b/fs/verity/signature.c
> index 0302a4e506ec..890d33b9d812 100644
> --- a/fs/verity/signature.c
> +++ b/fs/verity/signature.c
> @@ -67,7 +67,7 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
>                 return 0;
>         }
>
> -       if (fsverity_keyring->keys.nr_leaves_on_tree == 0) {
> +       if (keyring_is_empty(fsverity_keyring)) {
>                 /*
>                  * The ".fs-verity" keyring is empty, due to builtin signatures
>                  * being supported by the kernel but not actually being used.
> diff --git a/include/linux/key.h b/include/linux/key.h
> index c4486e938a06..20ca43f5eab1 100644
> --- a/include/linux/key.h
> +++ b/include/linux/key.h
> @@ -439,6 +439,7 @@ extern int restrict_link_reject(struct key *keyring,
>                                 struct key *restriction_key);
>
>  extern int keyring_clear(struct key *keyring);
> +bool keyring_is_empty(const struct key *keyring);
>
>  extern key_ref_t keyring_search(key_ref_t keyring,
>                                 struct key_type *type,
> diff --git a/kernel/bpf/keys.c b/kernel/bpf/keys.c
> index bffc356839ac..24e0416abc99 100644
> --- a/kernel/bpf/keys.c
> +++ b/kernel/bpf/keys.c
> @@ -29,7 +29,7 @@ struct bpf_key *bpf_lookup_keyring(void)
>
>         if (!bpf_keyring)
>                 return NULL;
> -       if (!READ_ONCE(bpf_keyring->keys.nr_leaves_on_tree) ||
> +       if (keyring_is_empty(bpf_keyring) ||
>             !READ_ONCE(bpf_keyring->restrict_link))
>                 return NULL;
>
> diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> index 5281da9d5bf7..ac48d6204915 100644
> --- a/security/keys/keyring.c
> +++ b/security/keys/keyring.c
> @@ -443,6 +443,16 @@ static void keyring_destroy(struct key *keyring)
>         assoc_array_destroy(&keyring->keys, &keyring_assoc_array_ops);
>  }
>
> +/**
> + * keyring_is_empty - Check whether a keyring is empty
> + * @keyring: The keyring to check.
> + */
> +bool keyring_is_empty(const struct key *keyring)
> +{
> +       return READ_ONCE(keyring->keys.nr_leaves_on_tree) == 0;
> +}
> +EXPORT_SYMBOL(keyring_is_empty);
> +
>  /*
>   * Describe a keyring for /proc.
>   */
> diff --git a/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh b/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
> index 1f9601ef22f8..792449d356cf 100755
> --- a/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
> +++ b/tools/testing/selftests/dm-verity/test-dm-verity-keyring.sh
> @@ -746,7 +746,7 @@ test_keyring_inactive_when_empty() {
>      log_info "TEST: Verify dm-verity keyring is inactive when sealed empty"
>
>      # When keyring_unsealed=0, the keyring is sealed immediately while empty
> -    # This means it should NOT be used for verification (nr_leaves_on_tree=0)
> +    # An empty keyring should NOT be used for verification.
>
>      log_info "Keyring state (should be empty and sealed):"
>      list_keyring_keys
> --
> 2.47.3
>
>