linux-kernel - [PATCH v3] mm: slub: avoid deref of free pointer in sanity checks if object is invalid

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Message-Id: <20250729081455.3311961-1-liqiong@nfschina.com>
Date: Tue, 29 Jul 2025 16:14:55 +0800
From: Li Qiong <liqiong@...china.com>
To: Christoph Lameter <cl@...two.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>,
	Harry Yoo <harry.yoo@...cle.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	Li Qiong <liqiong@...china.com>
Subject: [PATCH v3] mm: slub: avoid deref of free pointer in sanity checks if object is invalid

For debugging, object_err() prints free pointer of the object.
However, if check_valid_pointer() returns false for a object,
dereferncing `object + s->offset` can lead to a crash. Therefore,
print the object's address in such cases.

Fixes: bb192ed9aa71 ("mm/slub: Convert most struct page to struct slab by spatch")
Cc: <stable@...r.kernel.org>
Signed-off-by: Li Qiong <liqiong@...china.com>
---
v2:
- rephrase the commit message, add comment for object_err().
v3:
- check object pointer in object_err().
---
 mm/slub.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 31e11ef256f9..d3abae5a2193 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1104,7 +1104,11 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
 		return;
 
 	slab_bug(s, reason);
-	print_trailer(s, slab, object);
+	if (!check_valid_pointer(s, slab, object)) {
+		print_slab_info(slab);
+		pr_err("invalid object 0x%p\n", object);
+	} else
+		print_trailer(s, slab, object);
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
 	WARN_ON(1);
@@ -1587,7 +1591,7 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
 		return 0;
 
 	if (!check_valid_pointer(s, slab, object)) {
-		object_err(s, slab, object, "Freelist Pointer check fails");
+		slab_err(s, slab, "Freelist Pointer(0x%p) check fails", object);
 		return 0;
 	}
 
-- 
2.30.2