linux-kernel - [PATCH 3.10 011/250] tcp: avoid infinite loop in tcp_splice

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Message-Id: <1496876436-32402-12-git-send-email-w@1wt.eu>
Date:   Thu,  8 Jun 2017 00:56:37 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Eric Dumazet <edumazet@...gle.com>, Willy Tarreau <w@....eu>,
        "David S . Miller" <davem@...emloft.net>
Subject: [PATCH 3.10 011/250] tcp: avoid infinite loop in tcp_splice_read()

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>
Signed-off-by: Willy Tarreau <w@....eu>
---
 net/ipv4/tcp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5d4bd6c..d1e0422 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;
 				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);
-- 
2.8.0.rc2.1.gbe9624a