linux-kernel - [PATCH 3.18 04/13] tcp: clear icsk_backoff in tcp_write_queue

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Message-Id: <20190221125240.484240814@linuxfoundation.org>
Date:   Thu, 21 Feb 2019 15:35:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        soukjin bae <soukjin.bae@...sung.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.18 04/13] tcp: clear icsk_backoff in tcp_write_queue_purge()

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit 04c03114be82194d4a4858d41dba8e286ad1787c ]

soukjin bae reported a crash in tcp_v4_err() handling
ICMP_DEST_UNREACH after tcp_write_queue_head(sk)
returned a NULL pointer.

Current logic should have prevented this :

  if (seq != tp->snd_una  || !icsk->icsk_retransmits ||
      !icsk->icsk_backoff || fastopen)
      break;

Problem is the write queue might have been purged
and icsk_backoff has not been cleared.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: soukjin bae <soukjin.bae@...sung.com>
Acked-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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
@@ -1379,6 +1379,7 @@ static inline void tcp_write_queue_purge
 		sk_wmem_free_skb(sk, skb);
 	sk_mem_reclaim(sk);
 	tcp_clear_all_retrans_hints(tcp_sk(sk));
+	inet_csk(sk)->icsk_backoff = 0;
 }
 
 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2258,7 +2258,6 @@ int tcp_disconnect(struct sock *sk, int
 	tp->srtt_us = 0;
 	if ((tp->write_seq += tp->max_window + 2) == 0)
 		tp->write_seq = 1;
-	icsk->icsk_backoff = 0;
 	tp->snd_cwnd = 2;
 	icsk->icsk_probes_out = 0;
 	tp->packets_out = 0;