Re: [PATCH] apparmor: Fix label reference leak in aa_unix_file_perm()

[John Johansen <john.johansen@canonical.com>]

On 9/18/26 01:24, Greg KH wrote:
> On Thu, Sep 17, 2026 at 01:18:20PM -0700, John Johansen wrote:
>> On 9/17/26 12:19, Ryan Lee wrote:
>>> On Thu, Sep 17, 2026 at 11:59 AM Wentao Liang <vulab@iscas.ac.cn> wrote:
>>>>
>>>> The inner block in aa_unix_file_perm() re-declares plabel, shadowing the
>>>> outer variable that is released at the out label. The reference taken by
>>>> aa_get_label_rcu() is thus lost when the block exits, and aa_put_label()
>>>> at out is a no-op on the still NULL outer plabel, leaking one label per
>>>> permission check on a non-filesystem unix socket.
>>>>
>>>> Drop the shadowing declaration so the outer plabel is used and released.
>>>>
>>>> Fixes: 88fec3526e84 ("apparmor: make sure unix socket labeling is correctly updated.")
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
>>>> ---
>>>>    security/apparmor/af_unix.c | 1 -
>>>>    1 file changed, 1 deletion(-)
>>>>
>>>> diff --git a/security/apparmor/af_unix.c b/security/apparmor/af_unix.c
>>>> index fdb4a9f212c3..ecb40cfe7e14 100644
>>>> --- a/security/apparmor/af_unix.c
>>>> +++ b/security/apparmor/af_unix.c
>>>> @@ -758,7 +758,6 @@ int aa_unix_file_perm(const struct cred *subj_cred, struct aa_label *label,
>>>>                              unix_fs_perm(op, request, subj_cred, label,
>>>>                                           is_unix_fs(peer_sk) ? &peer_path : NULL));
>>>>           } else if (!is_sk_fs) {
>>>> -               struct aa_label *plabel;
>>>>                   struct aa_sk_ctx *pctx = aa_sock(peer_sk);
>>>>
>>>>                   rcu_read_lock();
>>>> --
>>>> 2.34.1
>>>>
>>>>
>>>
>>> NACK: this exact patch has been proposed before, and unfortunately
>>> exposes an additional latent bug around plabel handling that results
>>> in a use-after-free if the shadowed declaration is removed without
>>> additional fixes.
>>>
>>> I can try to dig out the relevant exchange from the AppArmor mailing
>>> list later, if you'd be interested.
>>>
>> The series Ryan is referring to is in Linus's tree, so you should see the
>> fix rolling out to stable kernels as well soon.
>>
>> 6d25e7b47616c apparmor: fix refcount leak when updating the sk_ctx
>> b1aea2c196077 apparmor: fix race in unix socket mediation when peer_path is used
>> 4483efe4f2151 apparmor: fix shadowing of plabel that prevents cache from being updated
> 
> These are all in stable released kernels already for many weeks, so how
> is any of this still being reported?
> 
> confused,
> I don't know, my guess is either using a distro kernel, or not having updated
to a newer stable kernel. I should not have said "stable", I should have said in
updated kernels.