linux-kernel - [PATCH] slub: Fix Off-By-One in the While condition in on

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Message-ID: <Z7DHXVNJ5aVBM2WA@Arch>
Date: Sat, 15 Feb 2025 18:57:01 +0200
From: Lilitha Persefoni Gkini <lilithpgkini@...il.com>
To: Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] slub: Fix Off-By-One in the While condition in on_freelist()

The condition `nr <= slab->objects` in the `on_freelist()` serves as
bound while walking through the `freelist` linked list because we can't
have more free objects than the maximum amount of objects in the slab.
But the `=` can result in an extra unnecessary iteration.

The patch changes it to `nr < slab->objects` to ensure it iterates
at most `slab->objects` number of times.

Signed-off-by: Lilitha Persefoni Gkini <lilithpgkini@...il.com>
---
 mm/slub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1f50129dcfb3..ad42450d4b0f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1435,7 +1435,7 @@ static int on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
 	int max_objects;
 
 	fp = slab->freelist;
-	while (fp && nr <= slab->objects) {
+	while (fp && nr < slab->objects) {
 		if (fp == search)
 			return 1;
 		if (!check_valid_pointer(s, slab, fp)) {
-- 
2.48.1