From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guillaume Nault Date: Mon, 15 Mar 2021 11:50:58 +0000 Subject: Re: [BUG] net/ppp: A use after free in ppp_unregister_channe Message-Id: <20210315115058.GA4296@linux.home> List-Id: References: <6057386d.ca12.1782148389e.Coremail.lyl2019@mail.ustc.edu.cn> In-Reply-To: <6057386d.ca12.1782148389e.Coremail.lyl2019@mail.ustc.edu.cn> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lyl2019@mail.ustc.edu.cn Cc: paulus@samba.org, davem@davemloft.net, linux-ppp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Parkin On Thu, Mar 11, 2021 at 08:34:44PM +0800, lyl2019@mail.ustc.edu.cn wrote: > File: drivers/net/ppp/ppp_generic.c > > In ppp_unregister_channel, pch could be freed in ppp_unbridge_channels() > but after that pch is still in use. Inside the function ppp_unbridge_channels, > if "pchbb = pch" is true and then pch will be freed. No. It's freed only if if the refcount drops to 0. And the caller of ppp_unregister_channel() must hold its own refcount. So ppp_unbridge_channels() is not going to drop the last refcount in this case. > I checked the commit history and found that this problem is introduced from > 4cf476ced45d7 ("ppp: add PPPIOCBRIDGECHAN and PPPIOCUNBRIDGECHAN ioctls"). Next time, please also Cc. the author of the patch. > I have no idea about how to generate a suitable patch, sorry. There's no patch to send as far as I can see.