linux-kernel - Re: [PATCH v1] fsnotify: Pass correct offset to fsnotify_mmap

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Message-ID: <66251c3e-4970-4cac-a1fc-46749d2a727a@arm.com>
Date: Mon, 6 Oct 2025 13:14:02 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Amir Goldstein <amir73il@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v1] fsnotify: Pass correct offset to fsnotify_mmap_perm()

On 06/10/2025 12:36, David Hildenbrand wrote:
> On 03.10.25 17:52, Ryan Roberts wrote:
>> fsnotify_mmap_perm() requires a byte offset for the file about to be
>> mmap'ed. But it is called from vm_mmap_pgoff(), which has a page offset.
>> Previously the conversion was done incorrectly so let's fix it, being
>> careful not to overflow on 32-bit platforms.
>>
>> Discovered during code review.
>>
>> Cc: <stable@...r.kernel.org>
>> Fixes: 066e053fe208 ("fsnotify: add pre-content hooks on mmap()")
>> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
>> ---
>> Applies against today's mm-unstable (aa05a436eca8).
>>
> 
> Curious: is there some easy way to write a reproducer? Did you look into that?

I didn't; this was just a drive-by discovery.

It looks like there are some fanotify tests in the filesystems selftests; I
guess they could be extended to add a regression test?

But FWIW, I think the kernel is just passing the ofset/length info off to user
space and isn't acting on it itself. So there is no kernel vulnerability here.

> 
> LGTM, thanks
> 
> Acked-by: David Hildenbrand <david@...hat.com>
>