net: datagram: fix unbounded loop in __skb_try_recv_datagram()

Christoph reported a stall while peeking datagram with an offset when
busy polling is enabled. __skb_try_recv_datagram() uses as the loop
termination condition 'queue empty'. When peeking, the socket
queue can be not empty, even when no additional packets are received.

Address the issue explicitly checking for receive queue changes,
as currently done by __skb_wait_for_more_packets().

Fixes: 2b5cd0dfa384 ("net: Change return type of sk_busy_loop from bool to void")
Reported-and-tested-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/datagram.c b/net/core/datagram.c
index b2651bb6d2a31dde065000c59bbbf3dfdadd976e..e657289db4ac44b023ce40ca9959185a6a33cb22 100644 (file)
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -279,7 +279,7 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
                        break;
 
                sk_busy_loop(sk, flags & MSG_DONTWAIT);
-       } while (!skb_queue_empty(&sk->sk_receive_queue));
+       } while (sk->sk_receive_queue.prev != *last);
 
        error = -EAGAIN;