netdev - Re: Kernel oops when clearing bgp neighbor info with TCP MD5SUM enabled

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Message-ID: <Pine.LNX.4.64.0910191745050.20086@sleet.zeugmasystems.local>
Date:	Mon, 19 Oct 2009 17:56:07 -0700 (PDT)
From:	Anirban Sinha <asinha@...gmasystems.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Anirban Sinha <ani@...rban.org>, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: Kernel oops when clearing bgp neighbor info with TCP MD5SUM
 enabled

> I'd suppose that this unbalance comes from inet_twdr_hangman() pathes.
>
> Could you verify this?

Yes, I have now verified this. There is indeed an issue with one of the
functions called by inet_twdr_hangman(). The call sequence is:

inet_twdr_hangman() -> inet_twdr_do_twkill_work() -> inet_twsk_put() ->
twsk_destructor().

In this case, the destructor callback is tcp_twsk_destructor() (installed
from line 1208 in net/ipv4/tcp_ipv4.c and line 906 in net/ipv6/tcp_ipv6.c) .
Without the TCP_MD5SUM compiled in, the function is a no-op. However, with the MD5SUM
compiled in, it calls tcp_put_md5_sig_pool() (when keylen is non zero) which
does an unbalanced put_cpu(). I did a grep across the entire tree.
tcp_put_md5_sig_pool() is a matching function for tcp_get_md5_sig_pool() and
in all other TCP IPV4 cases, it is called from net/ipv4/tcp_ipv4.c from
functions tcp_v4_md5_hash_hdr() and

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