On Wed, May 28, 2025 at 8:19 AM David Howells <dhowe...@redhat.com> wrote:
>
> Hi Linus,
>
> Could you apply this, please? There shouldn't be any functional change,
> rather it's a switch to using combined bit-barrier ops and lesser barriers.
> A better way to do this might be to provide set_bit_release(), but the end
> result would be much the same.
>
> Thanks,
> David
> ---
> From: Herbert Xu <herb...@gondor.apana.org.au>
>
> KEYS: Invert FINAL_PUT bit
>
> Invert the FINAL_PUT bit so that test_bit_acquire and clear_bit_unlock
> can be used instead of smp_mb.
>
> Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
> Signed-off-by: David Howells <dhowe...@redhat.com>
> Reviewed-by: Jarkko Sakkinen <jar...@kernel.org>
> cc: keyri...@vger.kernel.org
> cc: linux-security-mod...@vger.kernel.org
> cc: linux-crypto@vger.kernel.org
> cc: linux-integr...@vger.kernel.org
> ---
> include/linux/key.h | 2 +-
> security/keys/gc.c | 4 ++--
> security/keys/key.c | 5 +++--
> 3 files changed, 6 insertions(+), 5 deletions(-)
It doesn't look like this has made its way to Linus. David or Jarkko,
do one of you want to pick this up into a tree and send this to Linus
properly?
> diff --git a/include/linux/key.h b/include/linux/key.h
> index ba05de8579ec..81b8f05c6898 100644
> --- a/include/linux/key.h
> +++ b/include/linux/key.h
> @@ -236,7 +236,7 @@ struct key {
> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be
> invalidated by root without permission */
> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */
> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user
> session keyring */
> -#define KEY_FLAG_FINAL_PUT 10 /* set if final put has happened on
> key */
> +#define KEY_FLAG_USER_ALIVE 10 /* set if final put has not happened
> on key yet */
>
> /* the key type and key description string
> * - the desc is used to match a key against search criteria
> diff --git a/security/keys/gc.c b/security/keys/gc.c
> index f27223ea4578..748e83818a76 100644
> --- a/security/keys/gc.c
> +++ b/security/keys/gc.c
> @@ -218,8 +218,8 @@ static void key_garbage_collector(struct work_struct
> *work)
> key = rb_entry(cursor, struct key, serial_node);
> cursor = rb_next(cursor);
>
> - if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) {
> - smp_mb(); /* Clobber key->user after FINAL_PUT seen.
> */
> + if (!test_bit_acquire(KEY_FLAG_USER_ALIVE, &key->flags)) {
> + /* Clobber key->user after final put seen. */
> goto found_unreferenced_key;
> }
>
> diff --git a/security/keys/key.c b/security/keys/key.c
> index 7198cd2ac3a3..3bbdde778631 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -298,6 +298,7 @@ struct key *key_alloc(struct key_type *type, const char
> *desc,
> key->restrict_link = restrict_link;
> key->last_used_at = ktime_get_real_seconds();
>
> + key->flags |= 1 << KEY_FLAG_USER_ALIVE;
> if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
> key->flags |= 1 << KEY_FLAG_IN_QUOTA;
> if (flags & KEY_ALLOC_BUILT_IN)
> @@ -658,8 +659,8 @@ void key_put(struct key *key)
> key->user->qnbytes -= key->quotalen;
> spin_unlock_irqrestore(&key->user->lock,
> flags);
> }
> - smp_mb(); /* key->user before FINAL_PUT set. */
> - set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
> + /* Mark key as safe for GC after key->user done. */
> + clear_bit_unlock(KEY_FLAG_USER_ALIVE, &key->flags);
> schedule_work(&key_gc_work);
> }
> }
>
>
--
paul-moore.com
