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Date:   Thu, 28 May 2020 22:34:07 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     <jmaloy@...hat.com>, <ying.xue@...driver.com>,
        <davem@...emloft.net>, <kuba@...nel.org>,
        <tuong.t.lien@...tech.com.au>
CC:     <netdev@...r.kernel.org>, <tipc-discussion@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, YueHaibing <yuehaibing@...wei.com>
Subject: [PATCH net-next] tipc: Fix NULL pointer dereference in __tipc_sendstream()

tipc_sendstream() may send zero length packet, then tipc_msg_append()
do not alloc skb, skb_peek_tail() will get NULL, msg_set_ack_required
will trigger NULL pointer dereference.

Reported-by: syzbot+8eac6d030e7807c21d32@...kaller.appspotmail.com
Fixes: 0a3e060f340d ("tipc: add test for Nagle algorithm effectiveness")
Signed-off-by: YueHaibing <yuehaibing@...wei.com>
---
 net/tipc/socket.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index d6b67d07d22e..2943561399f1 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -1588,8 +1588,12 @@ static int __tipc_sendstream(struct socket *sock, struct msghdr *m, size_t dlen)
 				tsk->pkt_cnt += skb_queue_len(txq);
 			} else {
 				skb = skb_peek_tail(txq);
-				msg_set_ack_required(buf_msg(skb));
-				tsk->expect_ack = true;
+				if (skb) {
+					msg_set_ack_required(buf_msg(skb));
+					tsk->expect_ack = true;
+				} else {
+					tsk->expect_ack = false;
+				}
 				tsk->msg_acc = 0;
 				tsk->pkt_cnt = 0;
 			}
-- 
2.17.1


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