From dabc3e291d56e3125113101bc6d53d1a1738294d Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 6 Aug 2020 23:18:24 -0700 Subject: mm/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 [keescook@chromium.org: fix misplaced __free_one()] Link: http://lkml.kernel.org/r/202006261306.0D82A2B@keescook Link: https://lore.kernel.org/lkml/7ff248c7-d447-340c-a8e2-8c02972aca70@infradead.org Signed-off-by: Kees Cook Signed-off-by: Andrew Morton Acked-by: Vlastimil Babka Acked-by: Randy Dunlap [build tested] Cc: Roman Gushchin Cc: Christoph Lameter Cc: Alexander Popov Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Vinayak Menon Cc: Matthew Garrett Cc: Jann Horn Cc: Vijayanand Jitta Link: http://lkml.kernel.org/r/20200625215548.389774-3-keescook@chromium.org Signed-off-by: Linus Torvalds --- mm/slab.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'mm/slab.c') diff --git a/mm/slab.c b/mm/slab.c index 9350062ffc1a..77e90f9de9c0 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -588,6 +588,16 @@ static int transfer_objects(struct array_cache *to, return nr; } +/* &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; +} + #ifndef CONFIG_NUMA #define drain_alien_cache(cachep, alien) do { } while (0) @@ -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); } /** -- cgit