This is a note to let you know that I've just added the patch titled mm/slub: fix redzoning for small allocations to the 5.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-slub-fix-redzoning-for-small-allocations.patch and it can be found in the queue-5.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 74c1d3e081533825f2611e46edea1fcdc0701985 Mon Sep 17 00:00:00 2001 From: Kees Cook <keescook@xxxxxxxxxxxx> Date: Tue, 15 Jun 2021 18:23:22 -0700 Subject: mm/slub: fix redzoning for small allocations From: Kees Cook <keescook@xxxxxxxxxxxx> commit 74c1d3e081533825f2611e46edea1fcdc0701985 upstream. 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> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> 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: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/slab_common.c | 3 +-- mm/slub.c | 8 +++++--- 2 files changed, 6 insertions(+), 5 deletions(-) --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -89,8 +89,7 @@ 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 +++ b/mm/slub.c @@ -3732,15 +3732,17 @@ 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 stable-queue which might be from keescook@xxxxxxxxxxxx are queue-5.12/mm-slub.c-include-swab.h.patch queue-5.12/makefile-lto-pass-warn-stack-size-only-on-lld-13.0.0.patch queue-5.12/mm-slub-actually-fix-freelist-pointer-vs-redzoning.patch queue-5.12/mm-slub-clarify-verification-reporting.patch queue-5.12/mm-slub-fix-redzoning-for-small-allocations.patch