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

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Message-ID: <20251003155238.2147410-1-ryan.roberts@arm.com>
Date: Fri,  3 Oct 2025 16:52:36 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.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>
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH v1] fsnotify: Pass correct offset to fsnotify_mmap_perm()

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