[PATCH] keys: Avoid the owner account dereference in named keyring lookup

[sashiko-bot at kernel.org]

> Named keyring lookup must keep the storage containing the owner UID
> alive through the namespace mapping check.  find_keyring_by_name()
> reads keyring->user->uid under keyring_name_lock, but that lock protects
> the keyring's name entry and allocation, not its separate key_user.
> 
> A named session-keyring join can overlap a privileged KEYCTL_CHOWN on
> another CPU.  If the keyring holds the last reference to its old dynamic
> key_user and the ownership transfer succeeds, the following ordering is
> possible:
> 
>     Named join                         Chown
>     find_keyring_by_name()              keyctl_chown_key()
>       read_lock(keyring_name_lock)       down_write(key->sem)
>       load old keyring->user
>                                          replace key->user and key->uid
> [ ... ]
>     ==================================================================
> 
> Fixes: 2ea190d0a006 ("keys: skip keys from another user namespace")
> Assisted-by: LLM
> Signed-off-by: Cen Zhang <zzzccc427 at gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/pm-key-management-objects-candidate-0002-v2-dd6c20a1d92928b33ab7@gmail.com?part=1