linux-kernel - [PATCH 3.16 12/12] tcp: avoid infinite loop in tcp_splice

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Message-ID: <lsq.1487938201.139418242@decadent.org.uk>
Date:   Fri, 24 Feb 2017 12:10:01 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Dmitry Vyukov" <dvyukov@...gle.com>, "Willy Tarreau" <w@....eu>
Subject: [PATCH 3.16 12/12] tcp: avoid infinite loop in tcp_splice_read()

3.16.41-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@...gle.com>

commit ccf7abb93af09ad0868ae9033d1ca8108bdaec82 upstream.

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@...gle.com>
Reported-by: Dmitry Vyukov  <dvyukov@...gle.com>
Cc: Willy Tarreau <w@....eu>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv4/tcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -765,6 +765,12 @@ 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);
 			if (signal_pending(current)) {
 				ret = sock_intr_errno(timeo);