[PATCH 4.4 06/66] tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0

[Greg Kroah-Hartman]

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

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

From: Wei Wang <wei...@google.com>


[ Upstream commit 499350a5a6e7512d9ed369ed63a4244b6536f4f8 ]

When tcp_disconnect() is called, inet_csk_delack_init() sets
icsk->icsk_ack.rcv_mss to 0.
This could potentially cause tcp_recvmsg() => tcp_cleanup_rbuf() =>
__tcp_select_window() call path to have division by 0 issue.
So this patch initializes rcv_mss to TCP_MIN_MSS instead of 0.

Reported-by: Andrey Konovalov  <andreyk...@google.com>
Signed-off-by: Wei Wang <wei...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Yuchung Cheng <ych...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv4/tcp.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2260,6 +2260,10 @@ int tcp_disconnect(struct sock *sk, int
        tcp_set_ca_state(sk, TCP_CA_Open);
        tcp_clear_retrans(tp);
        inet_csk_delack_init(sk);
+       /* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0
+        * issue in __tcp_select_window()
+        */
+       icsk->icsk_ack.rcv_mss = TCP_MIN_MSS;
        tcp_init_send_head(sk);
        memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
        __sk_dst_reset(sk);