Subject: [PATCH] slab: Fix misplaced __free_one()

From: Kees Cook <[email-masked]>
Date: Fri, 26 Jun 2020 13:07:53 -0700

The implementation of __free_one() was accidentally placed inside a
CONFIG_NUMA #ifdef. Move it above.

Reported-by: Randy Dunlap <[email-masked]>
Link: https://lore.kernel.org/lkml/[email-masked]
Signed-off-by: Kees Cook <[email-masked]>
---
This a fix for slab-add-naive-detection-of-double-free.patch
---
 mm/slab.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index bbff6705ab2b..5ccb151a6e8f 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -588,6 +588,16 @@ static int transfer_objects(struct array_cache *to,
 	return nr;
 }
 
+/* &alien->lock must be held by alien callers. */
+static __always_inline void __free_one(struct array_cache *ac, void *objp)
+{
+	/* Avoid trivial double-free. */
+	if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
+	    WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp))
+		return;
+	ac->entry[ac->avail++] = objp;
+}
+
 #ifndef CONFIG_NUMA
 
 #define drain_alien_cache(cachep, alien) do { } while (0)
@@ -749,16 +759,6 @@ static void drain_alien_cache(struct kmem_cache *cachep,
 	}
 }
 
-/* &alien->lock must be held by alien callers. */
-static __always_inline void __free_one(struct array_cache *ac, void *objp)
-{
-	/* Avoid trivial double-free. */
-	if (IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
-	    WARN_ON_ONCE(ac->avail > 0 && ac->entry[ac->avail - 1] == objp))
-		return;
-	ac->entry[ac->avail++] = objp;
-}
-
 static int __cache_free_alien(struct kmem_cache *cachep, void *objp,
 				int node, int page_node)
 {
-- 
2.25.1

-- 
Kees Cook