linux-kernel - Re: [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign

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] [day] [month] [year] [list]

Message-ID: <CAHbLzkqeU0eufPEw-dHJ6vGPWncHffa6NuxeihWOjWknDryD4g@mail.gmail.com>
Date:   Wed, 1 Feb 2023 09:21:27 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Jan Kara <jack@...e.cz>, Shakeel Butt <shakeelb@...gle.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Ma Wupeng <mawupeng1@...wei.com>
Subject: Re: [PATCH] mm: memcg: fix NULL pointer in mem_cgroup_track_foreign_dirty()

On Wed, Feb 1, 2023 at 12:07 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Mon 30-01-23 11:30:47, Yang Shi wrote:
> > On Mon, Jan 30, 2023 at 4:20 AM Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> > >
> > >
> > >
> > > On 2023/1/30 16:48, Michal Hocko wrote:
> > > > On Mon 30-01-23 09:16:13, Kefeng Wang wrote:
> > > >>
> > > >>
> > > >> On 2023/1/30 5:48, Andrew Morton wrote:
> > > >>> On Sun, 29 Jan 2023 10:44:51 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> > > >>>
> > > >>>> As commit 18365225f044 ("hwpoison, memcg: forcibly uncharge LRU pages"),
> > > >>>
> > > >>> Merged in 2017.
> > > >>>
> > > >>>> hwpoison will forcibly uncharg a LRU hwpoisoned page, the folio_memcg
> > > >>>> could be NULl, then, mem_cgroup_track_foreign_dirty_slowpath() could
> > > >>>> occurs a NULL pointer dereference, let's do not record the foreign
> > > >>>> writebacks for folio memcg is null in mem_cgroup_track_foreign() to
> > > >>>> fix it.
> > > >>>>
> > > >>>> Reported-by: Ma Wupeng <mawupeng1@...wei.com>
> > > >>>> Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing")
> > > >>>
> > > >>> Merged in 2019.
> > > >>>
> > > ...
> > > >
> > > > Just to make sure I understand. The page has been hwpoisoned, uncharged
> > > > but stayed in the page cache so a next page fault on the address has blowned
> > > > up?
> > > >
> > > > Say we address the NULL memcg case. What is the resulting behavior?
> > > > Doesn't userspace access a poisoned page and get a silend memory
> > > > corruption?
> > >
> > > + Yang Shi
> > >
> > > Check previous link[1], seems that it is a known issue, and there is a
> > > TODO list for storage backed filesystems from Yang.
> >
> > For tmpfs and hugetlbfs, the page cache still stay in page cache, the
> > later page fault will handle the case gracefully. Other real storage
> > backed filesystem will have page cache truncated.
> >
> > The page cache will be uncharged before truncate. If the truncate
> > fails, we may end up in this case.
>
> This would be a good addendum to the changelog. What would be a typical
> failure in the truncation path?

For memory failure path, there may be a couple of cases, for example,
page is not for a regular file (maybe directory), fail to release
buffers, etc.

>
> > >
> > >
> > > [1]
> > > https://lore.kernel.org/all/20211020210755.23964-6-shy828301@gmail.com/T/#m1d40559ca2dcf94396df5369214288f69dec379b
>
> --
> Michal Hocko
> SUSE Labs