[PATCH 4.4 10/20] tcp: avoid infinite loop in tcp_splice_read()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>


[ Upstream commit ccf7abb93af09ad0868ae9033d1ca8108bdaec82 ]

Splicing from TCP socket is vulnerable when a packet with URG flag is
received and stored into receive queue.

__tcp_splice_read() returns 0, and sk_wait_data() immediately
returns since there is the problematic skb in queue.

This is a nice way to burn cpu (aka infinite loop) and trigger
soft lockups.

Again, this gem was found by syzkaller tool.

Fixes: 9c55e01c0cc8 ("[TCP]: Splice receive support.")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Dmitry Vyukov  <dvyukov@xxxxxxxxxx>
Cc: Willy Tarreau <w@xxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/tcp.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -783,6 +783,12 @@ ssize_t tcp_splice_read(struct socket *s
 				ret = -EAGAIN;
 				break;
 			}
+			/* if __tcp_splice_read() got nothing while we have
+			 * an skb in receive queue, we do not want to loop.
+			 * This might happen with URG data.
+			 */
+			if (!skb_queue_empty(&sk->sk_receive_queue))
+				break;
 			sk_wait_data(sk, &timeo, NULL);
 			if (signal_pending(current)) {
 				ret = sock_intr_errno(timeo);