phonet/pep: fix racy skb_queue_empty() use

[ Upstream commit 7d2a894d ]

The receive queues are protected by their respective spin-lock, not
the socket lock. This could lead to skb_peek() unexpectedly
returning NULL or a pointer to an already dequeued socket buffer.

Fixes: 9641458d ("Phonet: Pipe End Point for Phonet Pipes protocol")
Signed-off-by: Rémi Denis-Courmont <courmisch@gmail.com>
Link: https://lore.kernel.org/r/20240218081214.4806-2-remi@remlab.net


Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[Harshit: backport to 5.15.y, clean cherrypick from 6.1.y commit]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>