mm: ksize() should silently accept a NULL pointer

Other mm routines such as kfree() and kzfree() silently do the right thing
if passed a NULL pointer, so ksize() should do the same.
Signed-off-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200616225409.4670-1-william.kucharski@oracle.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab_common.c

@@ -1681,10 +1681,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 					   gfp_t flags)
 {
 	void *ret;
-	size_t ks = 0;
+	size_t ks;
 
-	if (p)
-		ks = ksize(p);
+	ks = ksize(p);
 
 	if (ks >= new_size) {
 		p = kasan_krealloc((void *)p, new_size, flags);
@@ -1744,10 +1743,9 @@ void kfree_sensitive(const void *p)
 	size_t ks;
 	void *mem = (void *)p;
 
-	if (unlikely(ZERO_OR_NULL_PTR(mem)))
-		return;
 	ks = ksize(mem);
-	memzero_explicit(mem, ks);
+	if (ks)
+		memzero_explicit(mem, ks);
 	kfree(mem);
 }
 EXPORT_SYMBOL(kfree_sensitive);
@@ -1770,8 +1768,6 @@ size_t ksize(const void *objp)
 {
 	size_t size;
 
-	if (WARN_ON_ONCE(!objp))
-		return 0;
 	/*
 	 * We need to check that the pointed to object is valid, and only then
 	 * unpoison the shadow memory below. We use __kasan_check_read(), to
@@ -1785,7 +1781,7 @@ size_t ksize(const void *objp)
 	 * We want to perform the check before __ksize(), to avoid potentially
 	 * crashing in __ksize() due to accessing invalid metadata.
 	 */
-	if (unlikely(objp == ZERO_SIZE_PTR) || !__kasan_check_read(objp, 1))
+	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !__kasan_check_read(objp, 1))
 		return 0;
 
 	size = __ksize(objp);