From: Soheil Hassas Yeganeh <soh...@google.com>

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 <subas...@codeaurora.org>
Reported-by: Sami Farin <hvtaifwkbgefb...@gmail.com>
Tested-by: Sami Farin <hvtaifwkbgefb...@gmail.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Yuchung Cheng <ych...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com>
---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4fa3f812b9ff8..9ce1c726185eb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2368,6 +2368,7 @@ void tcp_write_queue_purge(struct sock *sk)
        INIT_LIST_HEAD(&tcp_sk(sk)->tsorted_sent_queue);
        sk_mem_reclaim(sk);
        tcp_clear_all_retrans_hints(tcp_sk(sk));
+       tcp_sk(sk)->packets_out = 0;
 }
 
 int tcp_disconnect(struct sock *sk, int flags)
@@ -2417,7 +2418,6 @@ int tcp_disconnect(struct sock *sk, int flags)
        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;
-- 
2.17.0.484.g0c8726318c-goog

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