[PATCH] TCP: zero out rx_opt in tcp_disconnect()

[PATCH] TCP: zero out rx_opt in tcp_disconnect()

[Aji_Srinivas]

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.

Signed-off-by: Srinivas Aji <Aji_Srinivas@emc.com>
---
 net/ipv4/tcp.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index d6e4886..8b124ea 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -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);

Re: [PATCH] TCP: zero out rx_opt in tcp_disconnect()

[David Miller]

From: Aji_Srinivas@emc.com
Date: Thu, 3 May 2007 11:53:36 -0700

> 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.
> 
> Signed-off-by: Srinivas Aji <Aji_Srinivas@emc.com>

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.