tcp: fix recv with flags MSG_WAITALL | MSG_PEEK

Currently, tcp_recvmsg enters a busy loop in sk_wait_data if called
with flags = MSG_WAITALL | MSG_PEEK.

sk_wait_data waits for sk_receive_queue not empty, but in this case,
the receive queue is not empty, but does not contain any skb that we
can use.

Add a "last skb seen on receive queue" argument to sk_wait_data, so
that it sleeps until the receive queue has new skbs.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=99461
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=18493
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1205258
Reported-by: Enrico Scholz <rh-bugzilla@ensc.de>
Reported-by: Dan Searle <dan@censornet.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 2 deletions

diff --git a/net/core/sock.c b/net/core/sock.c
index 08f16db46070..8a14f1285fc4 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1967,20 +1967,21 @@ static void __release_sock(struct sock *sk)
  * sk_wait_data - wait for data to arrive at sk_receive_queue
  * @sk:    sock to wait on
  * @timeo: for how long
+ * @skb:   last skb seen on sk_receive_queue
  *
  * Now socket state including sk->sk_err is changed only under lock,
  * hence we may omit checks after joining wait queue.
  * We check receive queue before schedule() only as optimization;
  * it is very likely that release_sock() added new data.
  */
-int sk_wait_data(struct sock *sk, long *timeo)
+int sk_wait_data(struct sock *sk, long *timeo, const struct sk_buff *skb)
 {
         int rc;
         DEFINE_WAIT(wait);
 
         prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
         set_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);
-        rc = sk_wait_event(sk, timeo, !skb_queue_empty(&sk->sk_receive_queue));
+        rc = sk_wait_event(sk, timeo, skb_peek_tail(&sk->sk_receive_queue) != skb);
         clear_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags);
         finish_wait(sk_sleep(sk), &wait);
         return rc;