* [PATCH v4 2/3] mm/slub: Fix redzoning for small allocations
[not found] <20210608183955.280836-1-keescook@chromium.org>
@ 2021-06-08 18:39 ` Kees Cook
2021-06-11 9:13 ` Vlastimil Babka
2021-06-08 18:39 ` [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
1 sibling, 1 reply; 5+ messages in thread
From: Kees Cook @ 2021-06-08 18:39 UTC (permalink / raw
To: Andrew Morton
Cc: Kees Cook, stable, Vlastimil Babka, Marco Elver,
Christoph Lameter, Lin, Zhenpeng, Pekka Enberg, David Rientjes,
Joonsoo Kim, Roman Gushchin, linux-kernel, linux-doc, linux-mm
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.)
Fixes: 81819f0fc828 ("SLUB core")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
mm/slab_common.c | 3 +--
mm/slub.c | 8 +++++---
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index a4a571428c51..7cab77655f11 100644
--- a/mm/slab_common.c
+++ b/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;
}
diff --git a/mm/slub.c b/mm/slub.c
index f91d9fe7d0d8..f58cfd456548 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -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
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning
[not found] <20210608183955.280836-1-keescook@chromium.org>
2021-06-08 18:39 ` [PATCH v4 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
@ 2021-06-08 18:39 ` Kees Cook
2021-06-08 20:56 ` Andrew Morton
1 sibling, 1 reply; 5+ messages in thread
From: Kees Cook @ 2021-06-08 18:39 UTC (permalink / raw
To: Andrew Morton
Cc: Kees Cook, Marco Elver, Lin, Zhenpeng, stable, Vlastimil Babka,
Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Roman Gushchin, linux-kernel, linux-doc, linux-mm
It turns out that SLUB redzoning ("slub_debug=Z") checks from
s->object_size rather than from s->inuse (which is normally bumped
to make room for the freelist pointer), so a cache created with an
object size less than 24 would have the freelist pointer written beyond
s->object_size, causing the redzone to be corrupted by the freelist
pointer. This was very visible with "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____): 00 00 00 00 00 f6 f4 a5 ........
Redzone (____ptrval____): 40 1d e8 1a aa @....
Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........
Adjust the offset to stay within s->object_size.
(Note that no caches of in this size range are known to exist in the
kernel currently.)
Reported-by: Marco Elver <elver@google.com>
Reported-by: "Lin, Zhenpeng" <zplin@psu.edu>
Link: https://lore.kernel.org/linux-mm/20200807160627.GA1420741@elver.google.com/
Fixes: 89b83f282d8b (slub: avoid redzone when choosing freepointer location)
Cc: stable@vger.kernel.org
Tested-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/lkml/CANpmjNOwZ5VpKQn+SYWovTkFB4VsT-RPwyENBmaK0dLcpqStkA@mail.gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://lore.kernel.org/lkml/0f7dd7b2-7496-5e2d-9488-2ec9f8e90441@suse.cz/
---
mm/slub.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index f58cfd456548..fe30df460fad 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3689,7 +3689,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
{
slab_flags_t flags = s->flags;
unsigned int size = s->object_size;
- unsigned int freepointer_area;
unsigned int order;
/*
@@ -3698,13 +3697,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
* the possible location of the free pointer.
*/
size = ALIGN(size, sizeof(void *));
- /*
- * This is the area of the object where a freepointer can be
- * safely written. If redzoning adds more to the inuse size, we
- * can't use that portion for writing the freepointer, so
- * s->offset must be limited within this for the general case.
- */
- freepointer_area = size;
#ifdef CONFIG_SLUB_DEBUG
/*
@@ -3730,7 +3722,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
/*
* With that we have determined the number of bytes in actual use
- * by the object. This is the potential offset to the free pointer.
+ * by the object and redzoning.
*/
s->inuse = size;
@@ -3753,13 +3745,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
*/
s->offset = size;
size += sizeof(void *);
- } else if (freepointer_area > sizeof(void *)) {
+ } else {
/*
* Store freelist pointer near middle of object to keep
* it away from the edges of the object to avoid small
* sized over/underflows from neighboring allocations.
*/
- s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
+ s->offset = ALIGN_DOWN(s->object_size / 2, sizeof(void *));
}
#ifdef CONFIG_SLUB_DEBUG
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning
2021-06-08 18:39 ` [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
@ 2021-06-08 20:56 ` Andrew Morton
2021-06-08 23:11 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: Andrew Morton @ 2021-06-08 20:56 UTC (permalink / raw
To: Kees Cook
Cc: Marco Elver, Lin, Zhenpeng, stable, Vlastimil Babka,
Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Roman Gushchin, linux-kernel, linux-doc, linux-mm, Lin, Zhenpeng
On Tue, 8 Jun 2021 11:39:55 -0700 Kees Cook <keescook@chromium.org> wrote:
> It turns out that SLUB redzoning ("slub_debug=Z") checks from
> s->object_size rather than from s->inuse (which is normally bumped
> to make room for the freelist pointer), so a cache created with an
> object size less than 24 would have the freelist pointer written beyond
> s->object_size, causing the redzone to be corrupted by the freelist
> pointer. This was very visible with "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____): 00 00 00 00 00 f6 f4 a5 ........
> Redzone (____ptrval____): 40 1d e8 1a aa @....
> Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........
>
> Adjust the offset to stay within s->object_size.
>
> (Note that no caches of in this size range are known to exist in the
> kernel currently.)
We already have
https://lkml.kernel.org/r/6746FEEA-FD69-4792-8DDA-C78F5FE7DA02@psu.edu.
Is this patch better?
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3689,7 +3689,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> {
> slab_flags_t flags = s->flags;
> unsigned int size = s->object_size;
> - unsigned int freepointer_area;
> unsigned int order;
>
> /*
> @@ -3698,13 +3697,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> * the possible location of the free pointer.
> */
> size = ALIGN(size, sizeof(void *));
> - /*
> - * This is the area of the object where a freepointer can be
> - * safely written. If redzoning adds more to the inuse size, we
> - * can't use that portion for writing the freepointer, so
> - * s->offset must be limited within this for the general case.
> - */
> - freepointer_area = size;
>
> #ifdef CONFIG_SLUB_DEBUG
> /*
> @@ -3730,7 +3722,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>
> /*
> * With that we have determined the number of bytes in actual use
> - * by the object. This is the potential offset to the free pointer.
> + * by the object and redzoning.
> */
> s->inuse = size;
>
> @@ -3753,13 +3745,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> */
> s->offset = size;
> size += sizeof(void *);
> - } else if (freepointer_area > sizeof(void *)) {
> + } else {
> /*
> * Store freelist pointer near middle of object to keep
> * it away from the edges of the object to avoid small
> * sized over/underflows from neighboring allocations.
> */
> - s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
> + s->offset = ALIGN_DOWN(s->object_size / 2, sizeof(void *));
> }
>
> #ifdef CONFIG_SLUB_DEBUG
> --
> 2.25.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning
2021-06-08 20:56 ` Andrew Morton
@ 2021-06-08 23:11 ` Kees Cook
0 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2021-06-08 23:11 UTC (permalink / raw
To: Andrew Morton
Cc: Marco Elver, Lin, Zhenpeng, stable, Vlastimil Babka,
Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Roman Gushchin, linux-kernel, linux-doc, linux-mm
On Tue, Jun 08, 2021 at 01:56:33PM -0700, Andrew Morton wrote:
> On Tue, 8 Jun 2021 11:39:55 -0700 Kees Cook <keescook@chromium.org> wrote:
>
> > It turns out that SLUB redzoning ("slub_debug=Z") checks from
> > s->object_size rather than from s->inuse (which is normally bumped
> > to make room for the freelist pointer), so a cache created with an
> > object size less than 24 would have the freelist pointer written beyond
> > s->object_size, causing the redzone to be corrupted by the freelist
> > pointer. This was very visible with "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____): 00 00 00 00 00 f6 f4 a5 ........
> > Redzone (____ptrval____): 40 1d e8 1a aa @....
> > Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........
> >
> > Adjust the offset to stay within s->object_size.
> >
> > (Note that no caches of in this size range are known to exist in the
> > kernel currently.)
>
> We already have
> https://lkml.kernel.org/r/6746FEEA-FD69-4792-8DDA-C78F5FE7DA02@psu.edu.
> Is this patch better?
Yes, I believe so, since it reduces code and corrects the size checking
more directly (and more clearly demonstrates the redzone calculation
problem in the commit log).
-Kees
>
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -3689,7 +3689,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> > {
> > slab_flags_t flags = s->flags;
> > unsigned int size = s->object_size;
> > - unsigned int freepointer_area;
> > unsigned int order;
> >
> > /*
> > @@ -3698,13 +3697,6 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> > * the possible location of the free pointer.
> > */
> > size = ALIGN(size, sizeof(void *));
> > - /*
> > - * This is the area of the object where a freepointer can be
> > - * safely written. If redzoning adds more to the inuse size, we
> > - * can't use that portion for writing the freepointer, so
> > - * s->offset must be limited within this for the general case.
> > - */
> > - freepointer_area = size;
> >
> > #ifdef CONFIG_SLUB_DEBUG
> > /*
> > @@ -3730,7 +3722,7 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> >
> > /*
> > * With that we have determined the number of bytes in actual use
> > - * by the object. This is the potential offset to the free pointer.
> > + * by the object and redzoning.
> > */
> > s->inuse = size;
> >
> > @@ -3753,13 +3745,13 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> > */
> > s->offset = size;
> > size += sizeof(void *);
> > - } else if (freepointer_area > sizeof(void *)) {
> > + } else {
> > /*
> > * Store freelist pointer near middle of object to keep
> > * it away from the edges of the object to avoid small
> > * sized over/underflows from neighboring allocations.
> > */
> > - s->offset = ALIGN(freepointer_area / 2, sizeof(void *));
> > + s->offset = ALIGN_DOWN(s->object_size / 2, sizeof(void *));
> > }
> >
> > #ifdef CONFIG_SLUB_DEBUG
> > --
> > 2.25.1
--
Kees Cook
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4 2/3] mm/slub: Fix redzoning for small allocations
2021-06-08 18:39 ` [PATCH v4 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
@ 2021-06-11 9:13 ` Vlastimil Babka
0 siblings, 0 replies; 5+ messages in thread
From: Vlastimil Babka @ 2021-06-11 9:13 UTC (permalink / raw
To: Kees Cook, Andrew Morton
Cc: stable, Marco Elver, Christoph Lameter, Lin, Zhenpeng,
Pekka Enberg, David Rientjes, Joonsoo Kim, Roman Gushchin,
linux-kernel, linux-doc, linux-mm
On 6/8/21 8:39 PM, Kees Cook wrote:
> 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.)
>
> Fixes: 81819f0fc828 ("SLUB core")
> Cc: stable@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> mm/slab_common.c | 3 +--
> mm/slub.c | 8 +++++---
> 2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index a4a571428c51..7cab77655f11 100644
> --- a/mm/slab_common.c
> +++ b/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;
> }
> diff --git a/mm/slub.c b/mm/slub.c
> index f91d9fe7d0d8..f58cfd456548 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -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
>
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-06-08 18:39 ` [PATCH v4 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
2021-06-11 9:13 ` Vlastimil Babka
2021-06-08 18:39 ` [PATCH v4 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
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2021-06-08 23:11 ` Kees Cook
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