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

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

Message-ID: <8026c455-6237-47e3-98af-e3acb90dba25@suse.cz>
Date: Tue, 15 Jul 2025 12:23:31 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, akpm@...ux-foundation.org,
 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 7/15/25 11:52, David Hildenbrand wrote:
> On 15.07.25 11:40, Lorenzo Stoakes wrote:
>> 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.
> 
> When I skimmed that series the first time, I was wondering "why are we 
> even caring about PROCMAP_QUERY that in the context of this patch series".
> 
> Maybe that helps :)

Yeah seems like before patch 8/8 the ioctl handling, specifically
do_procmap_query() only looks at priv->mm and nothing else so it should be
safe as that's a stable value.

So it should be also enough to drop the last patch from mm for now, not
whole series.