[PATCH net] tcp: fix various issues for sockets morphing to listen state

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

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 <eduma...@google.com>
Reported-by: Dmitry Vyukov <dvyu...@google.com>
---
 net/ipv4/tcp_ipv4.c  |    7 +++++--
 net/ipv4/tcp_timer.c |    6 ++++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 
9a89b8deafae1e9b2e8d1d9bc211c9c30b8dd8ec..8f3ec1365497a58972d31d419f88b34457b5ae39
 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -279,10 +279,13 @@ 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;
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 
40d893556e6701ace6a02903e53c45822d6fa56d..b2ab411c6d3728fa7dbdebde045532a7317f5166
 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)) {