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

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Message-ID: <20251003155804.1571242-1-kirill@shutemov.name>
Date: Fri,  3 Oct 2025 16:58:04 +0100
From: Kiryl Shutsemau <kirill@...temov.name>
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>
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,
	Kiryl Shutsemau <kas@...nel.org>,
	stable@...r.kernel.org,
	Josef Bacik <josef@...icpanda.com>,
	Amir Goldstein <amir73il@...il.com>,
	Jan Kara <jack@...e.cz>
Subject: [PATCH] mm/mmap: Fix fsnotify_mmap_perm() call in vm_mmap_pgoff()

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);
 	if (!ret) {
 		if (mmap_write_lock_killable(mm))
 			return -EINTR;
-- 
2.50.1