linux-kernel - Re: [PATCH] mm/mmap: Fix fsnotify_mmap_perm() call in vm_mmap

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Message-ID: <cb93234b-9a4f-406b-9a82-04ced1453fc0@arm.com>
Date: Fri, 3 Oct 2025 22:37:56 +0530
From: Dev Jain <dev.jain@....com>
To: Kiryl Shutsemau <kas@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Ryan Roberts <ryan.roberts@....com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 Josef Bacik <josef@...icpanda.com>, Amir Goldstein <amir73il@...il.com>,
 Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] mm/mmap: Fix fsnotify_mmap_perm() call in vm_mmap_pgoff()

On 03/10/25 10:26 pm, Kiryl Shutsemau wrote:
> On Fri, Oct 03, 2025 at 04:58:04PM +0100, Kiryl Shutsemau wrote:
>> From: Kiryl Shutsemau <kas@...nel.org>
>>
>> vm_mmap_pgoff() includes a fsnotify call that allows for pre-content
>> hooks on mmap().
>>
>> The fsnotify_mmap_perm() function takes, among other arguments, an
>> offset in the file in the form of loff_t. However, vm_mmap_pgoff() has
>> file offset in the form of pgoff. This offset needs to be converted
>> before being passed to fsnotify_mmap_perm().
>>
>> The conversion from pgoff to loff_t is incorrect. The pgoff value needs
>> to be shifted left by PAGE_SHIFT to obtain loff_t, not right.
>>
>> This issue was identified through code inspection.
>>
>> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
>> Fixes: 066e053fe208 ("fsnotify: add pre-content hooks on mmap()")
>> Cc: stable@...r.kernel.org
>> Cc: Josef Bacik <josef@...icpanda.com>
>> Cc: Amir Goldstein <amir73il@...il.com>
>> Cc: Jan Kara <jack@...e.cz>
>> ---
>>   mm/util.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index f814e6a59ab1..52a667157264 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -573,7 +573,7 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
>>   
>>   	ret = security_mmap_file(file, prot, flag);
>>   	if (!ret)
>> -		ret = fsnotify_mmap_perm(file, prot, pgoff >> PAGE_SHIFT, len);
>> +		ret = fsnotify_mmap_perm(file, prot, pgoff << PAGE_SHIFT, len);
> It misses the case to (loff_t) and it broken for 32-bit machines.
>
> Luckily, Ryan submitted another fix for the same bug at the almost the
> same time. And he was more careful around types:
>
> https://lore.kernel.org/all/20251003155238.2147410-1-ryan.roberts@arm.com

Oops! I need to be more careful...

>