From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cyrill Gorcunov Date: Wed, 06 Jul 2016 08:26:02 +0000 Subject: Re: [Patch net] ppp: defer netns reference release for ppp channel Message-Id: <20160706082602.GM4666@uranus> List-Id: References: <1467781956-2229-1-git-send-email-xiyou.wangcong@gmail.com> In-Reply-To: <1467781956-2229-1-git-send-email-xiyou.wangcong@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Cong Wang Cc: netdev@vger.kernel.org, Matt.Bennett@alliedtelesis.co.nz, Paul Mackerras , linux-ppp@vger.kernel.org, Guillaume Nault On Tue, Jul 05, 2016 at 10:12:36PM -0700, Cong Wang wrote: > 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: 1f461dcdd296 ("ppp: take reference on channels netns") > Reported-by: Matt Bennett > Cc: Paul Mackerras > Cc: linux-ppp@vger.kernel.org > Cc: Guillaume Nault > Cc: Cyrill Gorcunov > Signed-off-by: Cong Wang > --- Hi Cong! I may be wrong, but this doesn't look right in general. We take the net in ppp_register_channel->ppp_register_net_channel and (name) context implies that ppp_unregister_channel does the reverse. Maybe there some sync point missed? I'll review in detail a bit later.