[PATCH] slab: redzone double-free detection
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>
diff --git a/mm/slab.c b/mm/slab.c
index 54bd2eb..2046da2 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2636,6 +2636,28 @@
}
}
+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 @@
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;
}