Messages in this thread Patch in this message | | | From | kpark3469@gmail ... | Subject | [PATCH] mm: slub: re-initialize randomized freelist sequence in calculate_sizes | Date | Sat, 8 Aug 2020 13:50:30 +0400 |
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From: Sahara <keun-o.park@digital14.com>
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.
Fixes: 210e7a43fa905 ("mm: SLUB freelist randomization") Reported-by: Ari-Pekka Verta <ari-pekka.verta@digital14.com> Reported-by: Timo Simola <timo.simola@digital14.com> Signed-off-by: Sahara <keun-o.park@digital14.com> --- mm/slub.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c index f226d66408ee..be1e4d6682b8 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3704,7 +3704,22 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order) 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) @@ -3748,12 +3763,6 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags) 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; -- 2.17.1
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