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>

5 files changed, 14 insertions, 10 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 05a8c1aea251..f21f0708ec59 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -902,7 +902,7 @@ void sk_stream_kill_queues(struct sock *sk);
 void sk_set_memalloc(struct sock *sk);
 void sk_clear_memalloc(struct sock *sk);
 
-int sk_wait_data(struct sock *sk, long *timeo);
+int sk_wait_data(struct sock *sk, long *timeo, const struct sk_buff *skb);
 
 struct request_sock_ops;
 struct timewait_sock_ops;
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;
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 52a94016526d..b5cf13a28009 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -886,7 +886,7 @@ verify_sock_status:
                         break;
                 }
 
-                sk_wait_data(sk, &timeo);
+                sk_wait_data(sk, &timeo, NULL);
                 continue;
         found_ok_skb:
                 if (len > skb->len)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7f4056785acc..45534a5ab430 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -780,7 +780,7 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
                                 ret = -EAGAIN;
                                 break;
                         }
-                        sk_wait_data(sk, &timeo);
+                        sk_wait_data(sk, &timeo, NULL);
                         if (signal_pending(current)) {
                                 ret = sock_intr_errno(timeo);
                                 break;
@@ -1575,7 +1575,7 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
         int target;             /* Read at least this many bytes */
         long timeo;
         struct task_struct *user_recv = NULL;
-        struct sk_buff *skb;
+        struct sk_buff *skb, *last;
         u32 urg_hole = 0;
 
         if (unlikely(flags & MSG_ERRQUEUE))
@@ -1635,7 +1635,9 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
 
                 /* Next get a buffer. */
 
+                last = skb_peek_tail(&sk->sk_receive_queue);
                 skb_queue_walk(&sk->sk_receive_queue, skb) {
+                        last = skb;
                         /* Now that we have two receive queues this
                          * shouldn't happen.
                          */
@@ -1754,8 +1756,9 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
                         /* Do not sleep, just process backlog. */
                         release_sock(sk);
                         lock_sock(sk);
-                } else
-                        sk_wait_data(sk, &timeo);
+                } else {
+                        sk_wait_data(sk, &timeo, last);
+                }
 
                 if (user_recv) {
                         int chunk;
diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 8fd9febaa5ba..8dab4e569571 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -613,7 +613,7 @@ static int llc_wait_data(struct sock *sk, long timeo)
                 if (signal_pending(current))
                         break;
                 rc = 0;
-                if (sk_wait_data(sk, &timeo))
+                if (sk_wait_data(sk, &timeo, NULL))
                         break;
         }
         return rc;
@@ -802,7 +802,7 @@ static int llc_ui_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
                         release_sock(sk);
                         lock_sock(sk);
                 } else
-                        sk_wait_data(sk, &timeo);
+                        sk_wait_data(sk, &timeo, NULL);
 
                 if ((flags & MSG_PEEK) && peek_seq != llc->copied_seq) {
                         net_dbg_ratelimited("LLC(%s:%d): Application bug, race in MSG_PEEK\n",