The patch titled
Subject: mm/slub: fix redzoning for small allocations
has been added to the -mm tree. Its filename is
mm-slub-fix-redzoning-for-small-allocations.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-slub-fix-redzoning-for-small-allocations.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-slub-fix-redzoning-for-small-allocations.patch
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------------------------------------------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: 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.)
Link: https://lkml.kernel.org/r/20210608183955.280836-3-keescook@xxxxxxxxxxxx
Fixes: 81819f0fc828 ("SLUB core")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: "Lin, Zhenpeng" <zplin@xxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab_common.c | 3 +--
mm/slub.c | 8 +++++---
2 files changed, 6 insertions(+), 5 deletions(-)
--- a/mm/slab_common.c~mm-slub-fix-redzoning-for-small-allocations
+++ a/mm/slab_common.c
@@ -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;
}
--- a/mm/slub.c~mm-slub-fix-redzoning-for-small-allocations
+++ a/mm/slub.c
@@ -3782,15 +3782,17 @@ static int calculate_sizes(struct kmem_c
*/
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
_
Patches currently in -mm which might be from keescook@xxxxxxxxxxxx are
mm-slub-clarify-verification-reporting.patch
mm-slub-fix-redzoning-for-small-allocations.patch
mm-slub-actually-fix-freelist-pointer-vs-redzoning.patch
