linux-kernel - [PATCH] Re: Kernel oops when clearing bgp neighbor info with TCP MD5SUM enabled

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Date:	Mon, 19 Oct 2009 18:08:21 -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: [PATCH] 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 tcp_v4_hash_skb() along with the matching
get()
function. So I would think that in tcp_twsk_destructor(), the call should be
replaced by  tcp_free_md5_sig_pool() instead.

Signed-of-by: Anirban Sinha <asinha@...gmasystems.com>
---

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

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index e48c37d..dccc01e 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -363,7 +363,7 @@ void tcp_twsk_destructor(struct sock *sk)
 #ifdef CONFIG_TCP_MD5SIG
        struct tcp_timewait_sock *twsk = tcp_twsk(sk);
        if (twsk->tw_md5_keylen)
-               tcp_put_md5sig_pool();
+               tcp_free_md5sig_pool();
 #endif
 }

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