FAILED: patch "[PATCH] mm/slub: fix redzoning for small allocations" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 74c1d3e081533825f2611e46edea1fcdc0701985 Mon Sep 17 00:00:00 2001
From: Kees Cook <[email protected]>
Date: Tue, 15 Jun 2021 18:23:22 -0700
Subject: [PATCH] mm/slub: fix redzoning for small allocations

The redzone area for SLUB exists between s->object_size and s->inuse (which is at least the word-aligned object_size). If a cache were created with an object_size smaller than sizeof(void *), the in-object stored freelist pointer would overwrite the redzone (e.g. with boot param "slub_debug=ZF"):

BUG test (Tainted: G B ): Right Redzone overwritten
-----------------------------------------------------------------------------

INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. First byte 0x1a instead of 0xbb
INFO: Slab 0xffffef3950b47000 objects=170 used=170 fp=0x0000000000000000 flags=0x8000000000000200
INFO: Object 0xffff957ead1c05d8 @offset=1496 fp=0xffff957ead1c0620

  Redzone  (____ptrval____): bb bb bb bb bb bb bb bb    ........
  Object   (____ptrval____): f6 f4 a5 40 1d e8          ...@..
  Redzone  (____ptrval____): 1a aa                      ..
  Padding  (____ptrval____): 00 00 00 00 00 00 00 00    ........

Store the freelist pointer out of line when object_size is smaller than sizeof(void *) and redzoning is enabled.

Additionally remove the "smaller than sizeof(void *)" check under CONFIG_DEBUG_VM in kmem_cache_sanity_check() as it is now redundant:
SLAB and SLOB both handle small sizes.

(Note that no caches within this size range are known to exist in the kernel currently.)

index a4a571428c51..7cab77655f11 100644
@@ -97,8 +97,7 @@ EXPORT_SYMBOL(kmem_cache_size);
 #ifdef CONFIG_DEBUG_VM
 static int kmem_cache_sanity_check(const char *name, unsigned int size)
 {
-	if (!name || in_interrupt() || size < sizeof(void *) ||
-		size > KMALLOC_MAX_SIZE) {
+	if (!name || in_interrupt() || size > KMALLOC_MAX_SIZE) {
 		pr_err("kmem_cache_create(%s) integrity check failed\n", name);
 		return -EINVAL;
 	}

index f91d9fe7d0d8..f58cfd456548 100644
@@ -3734,15 +3734,17 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 	 */
 	s->inuse = size;
 
-	if (((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
-		s->ctor)) {
+	if ((flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
+	    ((flags & SLAB_RED_ZONE) && s->object_size < sizeof(void *)) ||
+	    s->ctor) {
 		/*
 		 * Relocate free pointer after the object if it is not
 		 * permitted to overwrite the first word of the object on
 		 * kmem_cache_free.
 		 *
 		 * This is the case if we do RCU, have a constructor or
-		 * destructor or are poisoning the objects.
+		 * destructor, are poisoning the objects, or are
+		 * redzoning an object smaller than sizeof(void *).
 		 *
 		 * The assumption that s->offset >= s->inuse means free
 		 * pointer is outside of the object is used in the