linux-kernel - Re: [PATCH v6 7/8] fs/proc/task_mmu: read proc/pid/maps under per-vma lock

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 for Android: free password hash cracker in your pocket

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

Message-ID: <19d46c33-bd5e-41d1-88ad-3db071fa1bed@lucifer.local>
Date: Tue, 15 Jul 2025 10:40:38 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>, akpm@...ux-foundation.org,
        david@...hat.com, peterx@...hat.com, jannh@...gle.com,
        hannes@...xchg.org, mhocko@...nel.org, paulmck@...nel.org,
        shuah@...nel.org, adobriyan@...il.com, brauner@...nel.org,
        josef@...icpanda.com, yebin10@...wei.com, linux@...ssschuh.net,
        willy@...radead.org, osalvador@...e.de, andrii@...nel.org,
        ryan.roberts@....com, christophe.leroy@...roup.eu,
        tjmercier@...gle.com, kaleshsingh@...gle.com, aha310510@...il.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v6 7/8] fs/proc/task_mmu: read proc/pid/maps under
 per-vma lock

On Tue, Jul 15, 2025 at 10:16:41AM +0200, Vlastimil Babka wrote:
> > Andrew, could you please remove this patchset from mm-unstable for now
> > until I fix the issue and re-post the new version?
>
> Andrew can you do that please? We keep getting new syzbot reports.

I also pinged up top :P just to be extra specially clear...

>
> > The error I got after these fixes is:
>
> I suspect the root cause is the ioctls are not serialized against each other
> (probably not even against read()) and yet we treat m->private as safe to
> work on. Now we have various fields that are dangerous to race on - for
> example locked_vma and iter races would explain a lot of this.
>
> I suspect as long as we used purely seq_file workflow, it did the right
> thing for us wrt serialization, but the ioctl addition violates that. We
> should rather recheck even the code before this series, if dangerous ioctl
> vs read() races are possible. And the ioctl implementation should be
> refactored to use an own per-ioctl-call private context, not the seq_file's
> per-file-open context.

Entirely agree with this analysis. I had a look at most recent report, see:

https://lore.kernel.org/linux-mm/f13cda37-06a0-4281-87d1-042678a38a6b@lucifer.local/

AFAICT we either have to lock around the ioctl or find a new way of storing
per-ioctl state.

We'd probably need to separate out the procmap query stuff to do that
though. Probably.

I don't think a per-priv say lock is necessarily _that_ egregious since are
people _really_ opening this one file and doing multiple parallel queries all
that much?

Anyway this latest report seems entirely about the procmap stuff.