[PATCH 1/1] tcp: avoid infinite loop in tcp_splice_read()

Kleber Sacilotto de Souza kleber.souza at canonical.com
Fri Aug 25 11:03:55 UTC 2017

From: Eric Dumazet <edumazet at google.com>


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 at google.com>
Reported-by: Dmitry Vyukov  <dvyukov at google.com>
Cc: Willy Tarreau <w at 1wt.eu>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit ccf7abb93af09ad0868ae9033d1ca8108bdaec82)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
 net/ipv4/tcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index dd0655938f2d..16b5118d334f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -723,6 +723,12 @@ ssize_t tcp_splice_read(struct socket *sock, loff_t *ppos,
 				ret = -EAGAIN;
+			/* 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);

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