netdev - Re: [PATCH] TCP: zero out rx_opt in tcp

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Message-Id: <20070503.173157.41635650.davem@davemloft.net>
Date:	Thu, 03 May 2007 17:31:57 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	Aji_Srinivas@....com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] TCP: zero out rx_opt in tcp_disconnect()

From: Aji_Srinivas@....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@....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.

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