netdev - Re: [BUG] net/ppp: A use after free in ppp_unregister

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 15 Mar 2021 12:50:58 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     lyl2019@...l.ustc.edu.cn
Cc:     paulus@...ba.org, davem@...emloft.net, linux-ppp@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Parkin <tparkin@...alix.com>
Subject: Re: [BUG] net/ppp: A use after free in ppp_unregister_channe

On Thu, Mar 11, 2021 at 08:34:44PM +0800, lyl2019@...l.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.