On Sat, Aug 08, 2020 at 01:50:30PM +0400, kpark3...@gmail.com wrote: > From: Sahara <keun-o.p...@digital14.com>
Hi! > > 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 The problems here are actually larger than just the freelist pointers, so this was actually solved by just making these parameters not writable at runtime: https://git.kernel.org/linus/ad38b5b1131e2a0e5c46724847da2e1eba31fb68 I wonder if perhaps the above patch needs to be explicitly sent to the -stable trees? -Kees > ----------------------------------------------------------------------------- > > 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.ve...@digital14.com> > Reported-by: Timo Simola <timo.sim...@digital14.com> > Signed-off-by: Sahara <keun-o.p...@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 > -- Kees Cook
