Commit 7a2b4ee5 authored by WANG Cong's avatar WANG Cong Committed by Greg Kroah-Hartman

ppp: defer netns reference release for ppp channel

commit 205e1e25 upstream.

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: 1f461dcd ("ppp: take reference on channels netns")
Reported-by: default avatarMatt 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: default avatarCong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Cc: bmajal222 <bmajal222@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 37de955c
......@@ -2390,8 +2390,6 @@ ppp_unregister_channel(struct ppp_channel *chan)
spin_lock_bh(&pn->all_channels_lock);
list_del(&pch->list);
spin_unlock_bh(&pn->all_channels_lock);
put_net(pch->chan_net);
pch->chan_net = NULL;
pch->file.dead = 1;
wake_up_interruptible(&pch->file.rwait);
......@@ -2984,6 +2982,9 @@ ppp_disconnect_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);
if (!pch->file.dead) {
......
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