TCP: zero out rx_opt in tcp_disconnect()

When the server drops its connection, NFS client reconnects using the same socket after disconnecting. If the new connection's SYN,ACK doesn't contain the TCP timestamp option and the old connection's did, tp->tcp_header_len is recomputed assuming no timestamp header but tp->rx_opt.tstamp_ok remains set. Then tcp_build_and_update_options() adds in a timestamp option past the end of the allocated TCP header, overwriting TCP data, or when the data is in skb_shinfo(skb)->frags[], overwriting skb_shinfo(skb) causing a crash soon after. (The issue was debugged from such a crash.)

Similarly, wscale_ok and sack_ok also get set based on the SYN,ACK packet but not reset on disconnect, since they are zeroed out at initialization. The patch zeroes out the entire tp->rx_opt struct in tcp_disconnect() to avoid this sort of problem.

---
 net/ipv4/tcp.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

index d6e4886..8b124ea 100644
@@ -1760,8 +1760,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tcp_clear_retrans(tp);
 	inet_csk_delack_init(sk);
 	tcp_init_send_head(sk);
-	tp->rx_opt.saw_tstamp = 0;
-	tcp_sack_reset(&tp->rx_opt);
+	memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
 	__sk_dst_reset(sk);
 
 	BUG_TRAP(!inet->num || icsk->icsk_bind_hash);

From: [email protected]
Date: Thu, 3 May 2007 11:53:36 -0700

Thanks for catching this. It is rare to take advantage of the connect() with AF_UNSPEC feature that allows this.

Most applications close the socket and make a new one before connecting again.

I'll apply this fix, thanks a lot.