linux-kernel - [PATCH 9/9] mm: kmemleak: fix undetected leaks for page aligned objects

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Date:   Mon, 23 Jan 2023 11:04:19 -0600
From:   George Prekas <george@...abrica.net>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Andrei Vagin <avagin@...il.com>,
        George Prekas <george@...abrica.net>
Subject: [PATCH 9/9] mm: kmemleak: fix undetected leaks for page aligned objects

If kmalloc returns a page aligned object, then the object has 2
references: the pointer returned by kmalloc and page->s_mem of the first
page of the object. Account for this extra reference, so that kmemleak
can correctly detect leaks for page aligned objects.

Signed-off-by: George Prekas <george@...abrica.net>
---
 mm/slab.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/slab.h b/mm/slab.h
index 7cc432969945..76341c7c048e 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -734,6 +734,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
 					unsigned int orig_size)
 {
 	unsigned int zero_size = s->object_size;
+	int min_count;
 	size_t i;
 
 	flags &= gfp_allowed_mask;
@@ -761,7 +762,11 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
 		p[i] = kasan_slab_alloc(s, p[i], flags, init);
 		if (p[i] && init && !kasan_has_integrated_init())
 			memset(p[i], 0, zero_size);
-		kmemleak_alloc_recursive(p[i], s->object_size, 1,
+		min_count = 1;
+		/* If p[i] is page aligned, then a page->s_mem refers to it. */
+		if (((uintptr_t)p[i] & ~PAGE_MASK) == 0)
+			min_count++;
+		kmemleak_alloc_recursive(p[i], s->object_size, min_count,
 					 s->flags, flags);
 		kmsan_slab_alloc(s, p[i], flags);
 	}
-- 
2.37.1