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

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Message-ID: <24b1fc5c-32bc-45c4-beeb-f794e0fd0b79@lucifer.local>
Date: Tue, 14 Oct 2025 14:38:07 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.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>, 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 Fri, Oct 03, 2025 at 04:52:36PM +0100, 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.
>

Yikes, that's kind of crazy that has been in place for so long but not picked
up...

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

Thanks for fixing this!

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
> Applies against today's mm-unstable (aa05a436eca8).
>
> Thanks,
> Ryan
>
>
>  mm/util.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index 6c1d64ed0221..8989d5767528 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -566,6 +566,7 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
>  	unsigned long len, unsigned long prot,
>  	unsigned long flag, unsigned long pgoff)
>  {
> +	loff_t off = (loff_t)pgoff << PAGE_SHIFT;
>  	unsigned long ret;
>  	struct mm_struct *mm = current->mm;
>  	unsigned long populate;
> @@ -573,7 +574,7 @@ 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, off, len);
>  	if (!ret) {
>  		if (mmap_write_lock_killable(mm))
>  			return -EINTR;
> --
> 2.43.0
>