tcp: fix various issues for sockets morphing to listen state

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>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 40d893556e67..b2ab411c6d37 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -249,7 +249,8 @@ void tcp_delack_timer_handler(struct sock *sk)
 
         sk_mem_reclaim_partial(sk);
 
-        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
+        if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
+            !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
                 goto out;
 
         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
@@ -552,7 +553,8 @@ void tcp_write_timer_handler(struct sock *sk)
         struct inet_connection_sock *icsk = inet_csk(sk);
         int event;
 
-        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
+        if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
+            !icsk->icsk_pending)
                 goto out;
 
         if (time_after(icsk->icsk_timeout, jiffies)) {