[PATCH v4 3/3] KEYS: Verify the key identity in __key_unlink_begin

[sashiko-bot at kernel.org]

> When two keys have identical type and description, linking the second key
> replaces the first in a keyring. However, attempting to unlink the first
> key (no longer in the keyring) unlinks the second key.
> 
> This happens because __key_unlink_begin() calls assoc_array_delete() with
> &key->index_key, matching only on type and description rather than the
> key's identity.
> 
> Example:
> 
>   keyctl new_session >/dev/null
>   keyctl newring ring_a @s
>   keyctl newring ring_b @s
>   A=$(keyctl add user A ss %:ring_a)
>   B=$(keyctl add user A qq %:ring_b)
>   keyctl newring R @s
>   keyctl link $A %:R
>   keyctl link $B %:R
>   keyctl unlink $A %:R
>   keyctl show
> 
> Verify the key identity before unlinking, and return -ENOENT on mismatch,
> instead of unlinking the key with the wrong identity.
> 
> Cc: stable at vger.kernel.org
> Assisted-by: LLM
> Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
> Reviewed-by: David Howells <dhowells at redhat.com>
> Signed-off-by: Jarkko Sakkinen <jarkko at kernel.org>

Sashiko has reviewed this patch and found no issues.

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