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

[Dev Jain]

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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Fixes: 066e053fe208 ("fsnotify: add pre-content hooks on mmap()")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxx>
> > ---
> >   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@xxxxxxx

Oops! I need to be more careful...

>