tcp: fix various issues for sockets morphing to listen state

[ Upstream commit 02b2faaf0af1d85585f6d6980e286d53612acfc2 ]

Dmitry Vyukov reported a divide by 0 triggered by syzkaller, exploiting
tcp_disconnect() path that was never really considered and/or used
before syzkaller ;)

I was not able to reproduce the bug, but it seems issues here are the
three possible actions that assumed they would never trigger on a
listener.

1) tcp_write_timer_handler
2) tcp_delack_timer_handler
3) MTU reduction

Only IPv6 MTU reduction was properly testing TCP_CLOSE and TCP_LISTEN
 states from tcp_v6_mtu_reduced()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2259114c7242..5bb809f12ba1 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -269,10 +269,13 @@ EXPORT_SYMBOL(tcp_v4_connect);
  */
 void tcp_v4_mtu_reduced(struct sock *sk)
 {
-        struct dst_entry *dst;
         struct inet_sock *inet = inet_sk(sk);
-        u32 mtu = tcp_sk(sk)->mtu_info;
+        struct dst_entry *dst;
+        u32 mtu;
 
+        if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
+                return;
+        mtu = tcp_sk(sk)->mtu_info;
         dst = inet_csk_update_pmtu(sk, mtu);
         if (!dst)
                 return;