The patch titled
Subject: mm: slub: re-initialize randomized freelist sequence in calculate_sizes
has been added to the -mm tree. Its filename is
mm-slub-re-initialize-randomized-freelist-sequence-in-calculate_sizes.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-slub-re-initialize-randomized-freelist-sequence-in-calculate_sizes.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-slub-re-initialize-randomized-freelist-sequence-in-calculate_sizes.patch
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------------------------------------------------------
From: Sahara <keun-o.park@xxxxxxxxxxxxx>
Subject: mm: slub: re-initialize randomized freelist sequence in calculate_sizes
Slab cache flags are exported to sysfs and are allowed to get modified
from userspace. Some of those may call calculate_sizes function because
the changed flag can take an effect on slab object size and layout, which
means kmem_cache may have different order and objects. The freelist
pointer corruption occurs if some slab flags are modified while
CONFIG_SLAB_FREELIST_RANDOM is turned on.
$ echo 0 > /sys/kernel/slab/zs_handle/store_user
$ echo 0 > /sys/kernel/slab/zspage/store_user
$ mkswap /dev/block/zram0
$ swapon /dev/block/zram0 -p 32758
=============================================================================
BUG zs_handle (Not tainted): Freepointer corrupt
-----------------------------------------------------------------------------
Disabling lock debugging due to kernel taint
INFO: Slab 0xffffffbf29603600 objects=102 used=102 fp=0x0000000000000000 flags=0x0200
INFO: Object 0xffffffca580d8d78 @offset=3448 fp=0xffffffca580d8ed0
Redzone 00000000f3cddd6c: bb bb bb bb bb bb bb bb ........
Object 0000000082d5d74e: 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkk.
Redzone 000000008fd80359: bb bb bb bb bb bb bb bb ........
Padding 00000000c7f56047: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
In this example, an Android device tries to use zram as a swap and to turn
off store_user in order to reduce the slub object size. When
calculate_sizes is called in kmem_cache_open, size, order and objects for
zs_handle is:
size:360, order:0, objects:22
However, if the SLAB_STORE_USER bit is cleared in store_user_store:
size: 56, order:1, objects:73
All the size, order, and objects is changed by calculate_sizes(), but the
size of the random_seq array is still old value(22). As a result,
out-of-bound array access can occur at shuffle_freelist() when slab
allocation is requested.
This patch fixes the problem by re-allocating the random_seq array with
re-calculated correct objects value.
Link: https://lkml.kernel.org/r/20200808095030.13368-1-kpark3469@xxxxxxxxx
Fixes: 210e7a43fa905 ("mm: SLUB freelist randomization")
Reported-by: Ari-Pekka Verta <ari-pekka.verta@xxxxxxxxxxxxx>
Reported-by: Timo Simola <timo.simola@xxxxxxxxxxxxx>
Signed-off-by: Sahara <keun-o.park@xxxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slub.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
--- a/mm/slub.c~mm-slub-re-initialize-randomized-freelist-sequence-in-calculate_sizes
+++ a/mm/slub.c
@@ -3781,7 +3781,22 @@ static int calculate_sizes(struct kmem_c
if (oo_objects(s->oo) > oo_objects(s->max))
s->max = s->oo;
- return !!oo_objects(s->oo);
+ if (!oo_objects(s->oo))
+ return 0;
+
+ /*
+ * Initialize the pre-computed randomized freelist if slab is up.
+ * If the randomized freelist random_seq is already initialized,
+ * free and re-initialize it with re-calculated value.
+ */
+ if (slab_state >= UP) {
+ if (s->random_seq)
+ cache_random_seq_destroy(s);
+ if (init_cache_random_seq(s))
+ return 0;
+ }
+
+ return 1;
}
static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
@@ -3825,12 +3840,6 @@ static int kmem_cache_open(struct kmem_c
s->remote_node_defrag_ratio = 1000;
#endif
- /* Initialize the pre-computed randomized freelist if slab is up */
- if (slab_state >= UP) {
- if (init_cache_random_seq(s))
- goto error;
- }
-
if (!init_kmem_cache_nodes(s))
goto error;
_
Patches currently in -mm which might be from keun-o.park@xxxxxxxxxxxxx are
mm-slub-re-initialize-randomized-freelist-sequence-in-calculate_sizes.patch
