Re: [PATCH v1] fsnotify: Pass correct offset to fsnotify_mmap_perm()

[Ryan Roberts <ryan.roberts@arm.com>]

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@vger.kernel.org>
>> Fixes: 066e053fe208 ("fsnotify: add pre-content hooks on mmap()")
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.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@redhat.com>
>