mm/slub.c: fix wrong address during slab padding restoration

Start address calculated for slab padding restoration was wrong.  Wrong
address would point to some section before padding and could cause
corruption

Link: http://lkml.kernel.org/r/1516604578-4577-1-git-send-email-balasubramani_vivekanandan@mentor.com
Signed-off-by: Balasubramani Vivekanandan <balasubramani_vivekanandan@mentor.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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -838,6 +838,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 	u8 *start;
 	u8 *fault;
 	u8 *end;
+	u8 *pad;
 	int length;
 	int remainder;
 
@@ -851,8 +852,9 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 	if (!remainder)
 		return 1;
 
+	pad = end - remainder;
 	metadata_access_enable();
-	fault = memchr_inv(end - remainder, POISON_INUSE, remainder);
+	fault = memchr_inv(pad, POISON_INUSE, remainder);
 	metadata_access_disable();
 	if (!fault)
 		return 1;
@@ -860,9 +862,9 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 		end--;
 
 	slab_err(s, page, "Padding overwritten. 0x%p-0x%p", fault, end - 1);
-	print_section(KERN_ERR, "Padding ", end - remainder, remainder);
+	print_section(KERN_ERR, "Padding ", pad, remainder);
 
-	restore_bytes(s, "slab padding", POISON_INUSE, end - remainder, end);
+	restore_bytes(s, "slab padding", POISON_INUSE, fault, end);
 	return 0;
 }