From: Denis Lunev <den@openvz.org>
Date: Thu, 19 Apr 2007 00:05:58 +0000 (-0700)
Subject: [NETLINK]: Don't attach callback to a going-away netlink socket
X-Git-Tag: v2.6.21~58
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ac57b3a9ce280763296f99e32187a0b4384d9389;p=pandora-kernel.git

[NETLINK]: Don't attach callback to a going-away netlink socket

There is a race between netlink_dump_start() and netlink_release()
that can lead to the situation when a netlink socket with non-zero
callback is freed.

Here it is:

CPU1:                           CPU2
netlink_release():              netlink_dump_start():

                                sk = netlink_lookup(); /* OK */

netlink_remove();

spin_lock(&nlk->cb_lock);
if (nlk->cb) { /* false */
  ...
}
spin_unlock(&nlk->cb_lock);

                                spin_lock(&nlk->cb_lock);
                                if (nlk->cb) { /* false */
                                         ...
                                }
                                nlk->cb = cb;
                                spin_unlock(&nlk->cb_lock);
                                ...
sock_orphan(sk);
/*
 * proceed with releasing
 * the socket
 */

The proposal it to make sock_orphan before detaching the callback
in netlink_release() and to check for the sock to be SOCK_DEAD in
netlink_dump_start() before setting a new callback.

Signed-off-by: Denis Lunev <den@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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