Re: [PATCH] mm/mmap: Fix fsnotify_mmap_perm() call in vm_mmap_pgoff()

[Kiryl Shutsemau <kas@kernel.org>]

On Fri, Oct 03, 2025 at 04:58:04PM +0100, Kiryl Shutsemau wrote:
> From: Kiryl Shutsemau <kas@kernel.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@kernel.org>
> Fixes: 066e053fe208 ("fsnotify: add pre-content hooks on mmap()")
> Cc: stable@vger.kernel.org
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: Amir Goldstein <amir73il@gmail.com>
> Cc: Jan Kara <jack@suse.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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov