Slab allocators: fail if ksize is called with a NULL parameter

A NULL pointer means that the object was not allocated.  One cannot
determine the size of an object that has not been allocated.  Currently we
return 0 but we really should BUG() on attempts to determine the size of
something nonexistent.

krealloc() interprets NULL to mean a zero sized object.  Handle that
separately in krealloc().
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab.c

@@ -4446,7 +4446,8 @@ const struct seq_operations slabstats_op = {
  */
 size_t ksize(const void *objp)
 {
-	if (unlikely(ZERO_OR_NULL_PTR(objp)))
+	BUG_ON(!objp);
+	if (unlikely(objp == ZERO_SIZE_PTR))
 		return 0;
 
 	return obj_size(virt_to_cache(objp));

mm/slob.c

@@ -484,7 +484,8 @@ size_t ksize(const void *block)
 {
 	struct slob_page *sp;
 
-	if (unlikely(ZERO_OR_NULL_PTR(block)))
+	BUG_ON(!block);
+	if (unlikely(block == ZERO_SIZE_PTR))
 		return 0;
 
 	sp = (struct slob_page *)virt_to_page(block);

mm/slub.c

@@ -2449,7 +2449,8 @@ size_t ksize(const void *object)
 	struct page *page;
 	struct kmem_cache *s;
 
-	if (unlikely(ZERO_OR_NULL_PTR(object)))
+	BUG_ON(!object);
+	if (unlikely(object == ZERO_SIZE_PTR))
 		return 0;
 
 	page = get_object_page(object);

mm/util.c

@@ -81,14 +81,16 @@ EXPORT_SYMBOL(kmemdup);
 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 {
 	void *ret;
-	size_t ks;
+	size_t ks = 0;
 
 	if (unlikely(!new_size)) {
 		kfree(p);
 		return ZERO_SIZE_PTR;
 	}
 
-	ks = ksize(p);
+	if (p)
+		ks = ksize(p);
+
 	if (ks >= new_size)
 		return (void *)p;