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ppp: defer netns reference release for ppp channel 

Matt reported that we have a NULL pointer dereference
in ppp_pernet() from ppp_connect_channel(),
i.e. pch->chan_net is NULL.

This is due to that a parallel ppp_unregister_channel()
could happen while we are in ppp_connect_channel(), during
which pch->chan_net set to NULL. Since we need a reference
to net per channel, it makes sense to sync the refcnt
with the life time of the channel, therefore we should
release this reference when we destroy it.

Fixes: 1f461dcdd2 ("ppp: take reference on channels netns")
Reported-by: Matt Bennett <Matt.Bennett@alliedtelesis.co.nz>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linux-ppp@vger.kernel.org
Cc: Guillaume Nault <g.nault@alphalink.fr>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
WANG Cong 2016-07-05 22:12:36 -07:00 committed by David S. Miller
parent 06708f8152
commit 205e1e255c
1 changed files with 3 additions and 2 deletions
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5
drivers/net/ppp/ppp_generic.c
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@ -2601,8 +2601,6 @@ ppp_unregister_channel(struct ppp_channel *chan)
spin_lock_bh(&pn->all_channels_lock); spin_lock_bh(&pn->all_channels_lock);
list_del(&pch->list); list_del(&pch->list);
spin_unlock_bh(&pn->all_channels_lock); spin_unlock_bh(&pn->all_channels_lock);
put_net(pch->chan_net);
pch->chan_net = NULL;
pch->file.dead = 1; pch->file.dead = 1;
wake_up_interruptible(&pch->file.rwait); wake_up_interruptible(&pch->file.rwait);
@ -3136,6 +3134,9 @@ ppp_disconnect_channel(struct channel *pch)
*/ */
static void ppp_destroy_channel(struct channel *pch) static void ppp_destroy_channel(struct channel *pch)
{ {
put_net(pch->chan_net);
pch->chan_net = NULL;
atomic_dec(&channel_count); atomic_dec(&channel_count);
if (!pch->file.dead) { if (!pch->file.dead) {