commit 4c21daae3dbc9f8536cc18e6e53627821fa2c90c
author YueHaibing <yuehaibing@huawei.com> Thu May 28 22:34:07 2020 +0800
committer David S. Miller <davem@davemloft.net> Mon Jun 01 15:33:24 2020 -0700
tree 6fe27ee7cb67f7f769a420f7aa329bd1dd24d004
parent eae9d3c0167df840e821317040efcf0ca6789cb9

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@syzkaller.appspotmail.com
Fixes: 0a3e060f340d ("tipc: add test for Nagle algorithm effectiveness")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/socket.c

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 3734cdbe..26123f4 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;
 			}