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Date: Wed, 17 Jun 2020 12:53:49 -0700 From: Kees Cook <keescook@...omium.org> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Kees Cook <keescook@...omium.org>, Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <guro@...com>, Christoph Lameter <cl@...ux.com>, Alexander Popov <alex.popov@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, vinmenon@...eaurora.org, Matthew Garrett <mjg59@...gle.com>, Jann Horn <jannh@...gle.com>, Vijayanand Jitta <vjitta@...eaurora.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: [PATCH 2/2] slab: Add naive detection of double free Similar to commit ce6fa91b9363 ("mm/slub.c: add a naive detection of double free or corruption"), add a very cheap double-free check for SLAB under CONFIG_SLAB_FREELIST_HARDENED. With this added, the "SLAB_FREE_DOUBLE" LKDTM test passes under SLAB: lkdtm: Performing direct entry SLAB_FREE_DOUBLE lkdtm: Attempting double slab free ... ------------[ cut here ]------------ WARNING: CPU: 2 PID: 2193 at mm/slab.c:757 ___cache _free+0x325/0x390 Signed-off-by: Kees Cook <keescook@...omium.org> --- mm/slab.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/slab.c b/mm/slab.c index 9350062ffc1a..c4e3a194b271 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -749,6 +749,16 @@ static void drain_alien_cache(struct kmem_cache *cachep, } } +/* &alien->lock must be held by alien callers. */ +static __always_inline void __free_one(struct array_cache *ac, void *objp) +{ + /* Avoid trivial double-free. */ + if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && + WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp)) + return; + ac->entry[ac->avail++] = objp; +} + static int __cache_free_alien(struct kmem_cache *cachep, void *objp, int node, int page_node) { @@ -767,7 +777,7 @@ static int __cache_free_alien(struct kmem_cache *cachep, void *objp, STATS_INC_ACOVERFLOW(cachep); __drain_alien_cache(cachep, ac, page_node, &list); } - ac->entry[ac->avail++] = objp; + __free_one(ac, objp); spin_unlock(&alien->lock); slabs_destroy(cachep, &list); } else { @@ -3466,7 +3476,7 @@ void ___cache_free(struct kmem_cache *cachep, void *objp, } } - ac->entry[ac->avail++] = objp; + __free_one(ac, objp); } /** -- 2.25.1
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