From bffd168c3fc5cc7d2bad4c668fa90e7a9010db4b Mon Sep 17 00:00:00 2001
From: Soheil Hassas Yeganeh <soheil@google.com>
Date: Sat, 14 Apr 2018 20:44:46 -0400
Subject: [PATCH] tcp: clear tp->packets_out when purging write queue
Git-commit: bffd168c3fc5cc7d2bad4c668fa90e7a9010db4b
Patch-mainline: v4.17-rc2
References: bsc#1160560

Clear tp->packets_out when purging the write queue, otherwise
tcp_rearm_rto() mistakenly assumes TCP write queue is not empty.
This results in NULL pointer dereference.

Also, remove the redundant `tp->packets_out = 0` from
tcp_disconnect(), since tcp_disconnect() calls
tcp_write_queue_purge().

Fixes: a27fd7a8ed38 (tcp: purge write queue upon RST)
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Reported-by: Sami Farin <hvtaifwkbgefbaei@gmail.com>
Tested-by: Sami Farin <hvtaifwkbgefbaei@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 include/net/tcp.h |    1 +
 net/ipv4/tcp.c    |    1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1579,6 +1579,7 @@ static inline void tcp_write_queue_purge
 	sk_mem_reclaim(sk);
 	tcp_clear_all_retrans_hints(tcp_sk(sk));
 	tcp_init_send_head(sk);
+	tcp_sk(sk)->packets_out = 0;
 }
 
 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2226,7 +2226,6 @@ int tcp_disconnect(struct sock *sk, int
 	icsk->icsk_backoff = 0;
 	tp->snd_cwnd = 2;
 	icsk->icsk_probes_out = 0;
-	tp->packets_out = 0;
 	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_cnt = 0;
 	tp->window_clamp = 0;