slab: don't put freepointer outside of object if only orig_size

The commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra
allocated kmalloc space than requested") will extend right redzone
when allocating for orig_size < object_size. So we can't overlay the
freepointer in the object space in this case.

But the code looks like it forgot to check SLAB_RED_ZONE, since there
won't be extended right redzone if only orig_size enabled.

As we are here, make this complex conditional expressions a little
prettier and add some comments about extending right redzone when
slub_debug_orig_size() enabled.

Reviewed-by: Feng Tang <feng.tang@intel.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/mm/slub.c b/mm/slub.c
index 5df8c8302784d0f22784df72fba49bac92bea0f1..5fc052a4f38f3e3b8c1a6db8f1554d6e276d31f4 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5167,10 +5167,9 @@ static int calculate_sizes(struct kmem_cache *s)
         */
        s->inuse = size;
 
-       if (slub_debug_orig_size(s) ||
-           (flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
-           ((flags & SLAB_RED_ZONE) && s->object_size < sizeof(void *)) ||
-           s->ctor) {
+       if ((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) || s->ctor ||
+           ((flags & SLAB_RED_ZONE) &&
+            (s->object_size < sizeof(void *) || slub_debug_orig_size(s)))) {
                /*
                 * Relocate free pointer after the object if it is not
                 * permitted to overwrite the first word of the object on
@@ -5178,7 +5177,9 @@ static int calculate_sizes(struct kmem_cache *s)
                 *
                 * This is the case if we do RCU, have a constructor or
                 * destructor, are poisoning the objects, or are
-                * redzoning an object smaller than sizeof(void *).
+                * redzoning an object smaller than sizeof(void *) or are
+                * redzoning an object with slub_debug_orig_size() enabled,
+                * in which case the right redzone may be extended.
                 *
                 * The assumption that s->offset >= s->inuse means free
                 * pointer is outside of the object is used in the