linux-kernel - [PATCH 7/9] mm: kmemleak: erase page->s_mem in slab

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Date:   Mon, 23 Jan 2023 11:04:17 -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 7/9] mm: kmemleak: erase page->s_mem in slab_destroy

The field s_mem of struct page is initialized with the virtual address
of the page in function alloc_slabmgmt. If kmalloc allocates an object
that starts on this page, then kmemleak knows that this object has 2
references. On slab_destroy, s_mem should not continue referring to any
allocated object in the future.

Specifically, assume that initially the 4KB cache uses page[5] and its
s_mem = 0x5000. Then assume that this cache releases page[5] and the 8KB
cache allocates page[4] and page[5]. Subsequently, kmalloc returns an
8KB object at address 0x4000 which will have 3 references: the returned
pointer from kmalloc, page[4].s_mem = 0x4000, and page[5].s_mem. This
object can leak without detection.

Signed-off-by: George Prekas <george@...abrica.net>
---
 mm/slab.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/slab.c b/mm/slab.c
index a927e1a285d1..aa5eb725ee9c 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1611,6 +1611,9 @@ static void slab_destroy(struct kmem_cache *cachep, struct slab *slab)
 {
 	void *freelist;

+	/* Erase the page's virtual address from s_mem */
+	kmemleak_erase(&slab->s_mem);
+
 	freelist = slab->freelist;
 	slab_destroy_debugcheck(cachep, slab);
 	if (unlikely(cachep->flags & SLAB_TYPESAFE_BY_RCU))
-- 
2.37.1