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[PATCH] slab: redzone double-free detection

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At present our slab debugging tells us that it detected a double-free or
corruption - it does not distinguish between them.  Sometimes it's useful
to be able to differentiate between these two types of information.

Add double-free detection to redzone verification when freeing an object.
As explained by Manfred, when we are freeing an object, both redzones
should be RED_ACTIVE.  However, if both are RED_INACTIVE, we are trying to
free an object that was already free'd.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Pekka Enberg 2006-06-23 02:03:24 -07:00 committed by Linus Torvalds
parent b344e05c58
commit 58ce1fd580
1 changed files with 23 additions and 9 deletions
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32
mm/slab.c
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@ -2636,6 +2636,28 @@ static void kfree_debugcheck(const void *objp)
}
}
static inline void verify_redzone_free(struct kmem_cache *cache, void *obj)
{
unsigned long redzone1, redzone2;
redzone1 = *dbg_redzone1(cache, obj);
redzone2 = *dbg_redzone2(cache, obj);
/*
* Redzone is ok.
*/
if (redzone1 == RED_ACTIVE && redzone2 == RED_ACTIVE)
return;
if (redzone1 == RED_INACTIVE && redzone2 == RED_INACTIVE)
slab_error(cache, "double free detected");
else
slab_error(cache, "memory outside object was overwritten");
printk(KERN_ERR "%p: redzone 1:0x%lx, redzone 2:0x%lx.\n",
obj, redzone1, redzone2);
}
static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
void *caller)
{
@ -2659,15 +2681,7 @@ static void *cache_free_debugcheck(struct kmem_cache *cachep, void *objp,
slabp = page_get_slab(page);
if (cachep->flags & SLAB_RED_ZONE) {
if (*dbg_redzone1(cachep, objp) != RED_ACTIVE ||
*dbg_redzone2(cachep, objp) != RED_ACTIVE) {
slab_error(cachep, "double free, or memory outside"
" object was overwritten");
printk(KERN_ERR "%p: redzone 1:0x%lx, "
"redzone 2:0x%lx.\n",
objp, *dbg_redzone1(cachep, objp),
*dbg_redzone2(cachep, objp));
}
verify_redzone_free(cachep, objp);
*dbg_redzone1(cachep, objp) = RED_INACTIVE;
*dbg_redzone2(cachep, objp) = RED_INACTIVE;
}