* [PATCH v2 1/3] mm/slub: Clarify verification reporting
2020-10-09 19:54 [PATCH v2 0/3] Actually fix freelist pointer vs redzoning Kees Cook
@ 2020-10-09 19:54 ` Kees Cook
2020-10-13 16:13 ` Vlastimil Babka
2020-10-09 19:54 ` [PATCH v2 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
2020-10-09 19:54 ` [PATCH v2 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
2 siblings, 1 reply; 8+ messages in thread
From: Kees Cook @ 2020-10-09 19:54 UTC (permalink / raw)
To: Andrew Morton
Cc: Kees Cook, Marco Elver, Jonathan Corbet, Christoph Lameter,
Pekka Enberg, David Rientjes, Joonsoo Kim, Vlastimil Babka,
Roman Gushchin, linux-kernel, linux-doc, linux-mm
Instead of repeating "Redzone" and "Poison", clarify which sides of
those zones got tripped. Additionally fix column alignment in the
trailer.
Before:
BUG test (Tainted: G B ): Redzone overwritten
...
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 ........
After:
BUG test (Tainted: G B ): Right Redzone overwritten
...
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 ........
Fixes: d86bd1bece6f ("mm/slub: support left redzone")
Fixes: ffc79d288000 ("slub: use print_hex_dump")
Fixes: 2492268472e7 ("SLUB: change error reporting format to follow lockdep loosely")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
Documentation/vm/slub.rst | 10 +++++-----
mm/slub.c | 14 +++++++-------
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
index 289d231cee97..77c7a3331eda 100644
--- a/Documentation/vm/slub.rst
+++ b/Documentation/vm/slub.rst
@@ -181,7 +181,7 @@ SLUB Debug output
Here is a sample of slub debug output::
====================================================================
- BUG kmalloc-8: Redzone overwritten
+ BUG kmalloc-8: Right Redzone overwritten
--------------------------------------------------------------------
INFO: 0xc90f6d28-0xc90f6d2b. First byte 0x00 instead of 0xcc
@@ -189,10 +189,10 @@ Here is a sample of slub debug output::
INFO: Object 0xc90f6d20 @offset=3360 fp=0xc90f6d58
INFO: Allocated in get_modalias+0x61/0xf5 age=53 cpu=1 pid=554
- Bytes b4 0xc90f6d10: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
- Object 0xc90f6d20: 31 30 31 39 2e 30 30 35 1019.005
- Redzone 0xc90f6d28: 00 cc cc cc .
- Padding 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
+ Bytes b4 (0xc90f6d10): 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
+ Object (0xc90f6d20): 31 30 31 39 2e 30 30 35 1019.005
+ Redzone (0xc90f6d28): 00 cc cc cc .
+ Padding (0xc90f6d50): 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
[<c010523d>] dump_trace+0x63/0x1eb
[<c01053df>] show_trace_log_lvl+0x1a/0x2f
diff --git a/mm/slub.c b/mm/slub.c
index 6d3574013b2f..f4f1d63f0ab9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -698,15 +698,15 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
p, p - addr, get_freepointer(s, p));
if (s->flags & SLAB_RED_ZONE)
- print_section(KERN_ERR, "Redzone ", p - s->red_left_pad,
+ print_section(KERN_ERR, "Redzone ", p - s->red_left_pad,
s->red_left_pad);
else if (p > addr + 16)
print_section(KERN_ERR, "Bytes b4 ", p - 16, 16);
- print_section(KERN_ERR, "Object ", p,
+ print_section(KERN_ERR, "Object ", p,
min_t(unsigned int, s->object_size, PAGE_SIZE));
if (s->flags & SLAB_RED_ZONE)
- print_section(KERN_ERR, "Redzone ", p + s->object_size,
+ print_section(KERN_ERR, "Redzone ", p + s->object_size,
s->inuse - s->object_size);
off = get_info_end(s);
@@ -718,7 +718,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
if (off != size_from_object(s))
/* Beginning of the filler is the free pointer */
- print_section(KERN_ERR, "Padding ", p + off,
+ print_section(KERN_ERR, "Padding ", p + off,
size_from_object(s) - off);
dump_stack();
@@ -895,11 +895,11 @@ static int check_object(struct kmem_cache *s, struct page *page,
u8 *endobject = object + s->object_size;
if (s->flags & SLAB_RED_ZONE) {
- if (!check_bytes_and_report(s, page, object, "Redzone",
+ if (!check_bytes_and_report(s, page, object, "Left Redzone",
object - s->red_left_pad, val, s->red_left_pad))
return 0;
- if (!check_bytes_and_report(s, page, object, "Redzone",
+ if (!check_bytes_and_report(s, page, object, "Right Redzone",
endobject, val, s->inuse - s->object_size))
return 0;
} else {
@@ -914,7 +914,7 @@ static int check_object(struct kmem_cache *s, struct page *page,
if (val != SLUB_RED_ACTIVE && (s->flags & __OBJECT_POISON) &&
(!check_bytes_and_report(s, page, p, "Poison", p,
POISON_FREE, s->object_size - 1) ||
- !check_bytes_and_report(s, page, p, "Poison",
+ !check_bytes_and_report(s, page, p, "End Poison",
p + s->object_size - 1, POISON_END, 1)))
return 0;
/*
--
2.25.1
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH v2 2/3] mm/slub: Fix redzoning for small allocations
2020-10-09 19:54 [PATCH v2 0/3] Actually fix freelist pointer vs redzoning Kees Cook
2020-10-09 19:54 ` [PATCH v2 1/3] mm/slub: Clarify verification reporting Kees Cook
@ 2020-10-09 19:54 ` Kees Cook
2020-10-12 8:01 ` Christopher Lameter
2020-10-09 19:54 ` [PATCH v2 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
2 siblings, 1 reply; 8+ messages in thread
From: Kees Cook @ 2020-10-09 19:54 UTC (permalink / raw)
To: Andrew Morton
Cc: Kees Cook, stable, Marco Elver, Jonathan Corbet,
Christoph Lameter, Pekka Enberg, David Rientjes, Joonsoo Kim,
Vlastimil Babka, 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 will be overwritten by redzoning (e.g. with boot param
"slub_debug=ZV"):
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.
(Note that no caches with such a size 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/slub.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index f4f1d63f0ab9..752fad36522c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3682,15 +3682,17 @@ 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] 8+ messages in thread
* [PATCH v2 3/3] mm/slub: Actually fix freelist pointer vs redzoning
2020-10-09 19:54 [PATCH v2 0/3] Actually fix freelist pointer vs redzoning Kees Cook
2020-10-09 19:54 ` [PATCH v2 1/3] mm/slub: Clarify verification reporting Kees Cook
2020-10-09 19:54 ` [PATCH v2 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
@ 2020-10-09 19:54 ` Kees Cook
2020-10-13 16:44 ` Vlastimil Babka
2 siblings, 1 reply; 8+ messages in thread
From: Kees Cook @ 2020-10-09 19:54 UTC (permalink / raw)
To: Andrew Morton
Cc: Kees Cook, Marco Elver, Jonathan Corbet, Christoph Lameter,
Pekka Enberg, David Rientjes, Joonsoo Kim, Vlastimil Babka,
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 their freelist pointer written beyond
s->object_size, causing the redzone to corrupt 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.
Reported-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/linux-mm/20200807160627.GA1420741@elver.google.com/
Fixes: 89b83f282d8b (slub: avoid redzone when choosing freepointer location)
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>
---
mm/slub.c | 14 +++-----------
1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index 752fad36522c..6f115e56c5d0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3637,7 +3637,6 @@ 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;
/*
@@ -3646,13 +3645,6 @@ 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
/*
@@ -3678,7 +3670,7 @@ 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;
@@ -3701,13 +3693,13 @@ 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] 8+ messages in thread