From: Kees Cook <keescook@xxxxxxxxxxxx>
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@xxxxxxxxxxxx: fix misplaced __free_one()]
Link: http://lkml.kernel.org/r/202006261306.0D82A2B@keescook
Link: https://lore.kernel.org/lkml/7ff248c7-d447-340c-a8e2-8c02972aca70@xxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/20200625215548.389774-3-keescook@xxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> [build tested]
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Alexander Popov <alex.popov@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Cc: Matthew Garrett <mjg59@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- a/mm/slab.c~slab-add-naive-detection-of-double-free
+++ a/mm/slab.c
@@ -588,6 +588,16 @@ static int transfer_objects(struct array
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 kme
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 *ca
}
}
- ac->entry[ac->avail++] = objp;
+ __free_one(ac, objp);
}
/**
_
