From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cyrill Gorcunov Date: Wed, 06 Jul 2016 12:25:15 +0000 Subject: Re: [Patch net] ppp: defer netns reference release for ppp channel Message-Id: <20160706122515.GN4666@uranus> List-Id: References: <1467781956-2229-1-git-send-email-xiyou.wangcong@gmail.com> <20160706082602.GM4666@uranus> In-Reply-To: <20160706082602.GM4666@uranus> 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 Wed, Jul 06, 2016 at 11:26:02AM +0300, Cyrill Gorcunov wrote: > 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. After staring more I think the patch should be fine as a fix since implementing sync with ppp_[re|un]register_channel and ppp_ioctl might need a way more work. Reviewed-by: Cyrill Gorcunov