phonet/pep: fix racy skb_queue_empty() use

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: 9641458d3ec4 ("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>

diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index faba31f2eff2903bee7082b295f137ff848a1e10..3dd5f52bc1b58e3f1ee4e235126438c723f1f73c 100644 (file)
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -917,6 +917,37 @@ static int pep_sock_enable(struct sock *sk, struct sockaddr *addr, int len)
        return 0;
 }
 
+static unsigned int pep_first_packet_length(struct sock *sk)
+{
+       struct pep_sock *pn = pep_sk(sk);
+       struct sk_buff_head *q;
+       struct sk_buff *skb;
+       unsigned int len = 0;
+       bool found = false;
+
+       if (sock_flag(sk, SOCK_URGINLINE)) {
+               q = &pn->ctrlreq_queue;
+               spin_lock_bh(&q->lock);
+               skb = skb_peek(q);
+               if (skb) {
+                       len = skb->len;
+                       found = true;
+               }
+               spin_unlock_bh(&q->lock);
+       }
+
+       if (likely(!found)) {
+               q = &sk->sk_receive_queue;
+               spin_lock_bh(&q->lock);
+               skb = skb_peek(q);
+               if (skb)
+                       len = skb->len;
+               spin_unlock_bh(&q->lock);
+       }
+
+       return len;
+}
+
 static int pep_ioctl(struct sock *sk, int cmd, int *karg)
 {
        struct pep_sock *pn = pep_sk(sk);
@@ -929,15 +960,7 @@ static int pep_ioctl(struct sock *sk, int cmd, int *karg)
                        break;
                }
 
-               lock_sock(sk);
-               if (sock_flag(sk, SOCK_URGINLINE) &&
-                   !skb_queue_empty(&pn->ctrlreq_queue))
-                       *karg = skb_peek(&pn->ctrlreq_queue)->len;
-               else if (!skb_queue_empty(&sk->sk_receive_queue))
-                       *karg = skb_peek(&sk->sk_receive_queue)->len;
-               else
-                       *karg = 0;
-               release_sock(sk);
+               *karg = pep_first_packet_length(sk);
                ret = 0;
                break;