On 9/9/21 7:37 AM, Li Jinlin wrote:
> From: Li Jinlin <lijinlin3@xxxxxxxxxx>
>
> KASAN reports a use-after-free report when doing fuzz test:
>
> [693354.104835] ==================================================================
> [693354.105094] BUG: KASAN: use-after-free in bfq_io_set_weight_legacy+0xd3/0x160
> [693354.105336] Read of size 4 at addr ffff888be0a35664 by task sh/1453338
>
> [693354.105607] CPU: 41 PID: 1453338 Comm: sh Kdump: loaded Not tainted 4.18.0-147
> [693354.105610] Hardware name: Huawei 2288H V5/BC11SPSCB0, BIOS 0.81 07/02/2018
> [693354.105612] Call Trace:
> [693354.105621] dump_stack+0xf1/0x19b
> [693354.105626] ? show_regs_print_info+0x5/0x5
> [693354.105634] ? printk+0x9c/0xc3
> [693354.105638] ? cpumask_weight+0x1f/0x1f
> [693354.105648] print_address_description+0x70/0x360
> [693354.105654] kasan_report+0x1b2/0x330
> [693354.105659] ? bfq_io_set_weight_legacy+0xd3/0x160
> [693354.105665] ? bfq_io_set_weight_legacy+0xd3/0x160
> [693354.105670] bfq_io_set_weight_legacy+0xd3/0x160
> [693354.105675] ? bfq_cpd_init+0x20/0x20
> [693354.105683] cgroup_file_write+0x3aa/0x510
> [693354.105693] ? ___slab_alloc+0x507/0x540
> [693354.105698] ? cgroup_file_poll+0x60/0x60
> [693354.105702] ? 0xffffffff89600000
> [693354.105708] ? usercopy_abort+0x90/0x90
> [693354.105716] ? mutex_lock+0xef/0x180
> [693354.105726] kernfs_fop_write+0x1ab/0x280
> [693354.105732] ? cgroup_file_poll+0x60/0x60
> [693354.105738] vfs_write+0xe7/0x230
> [693354.105744] ksys_write+0xb0/0x140
> [693354.105749] ? __ia32_sys_read+0x50/0x50
> [693354.105760] do_syscall_64+0x112/0x370
> [693354.105766] ? syscall_return_slowpath+0x260/0x260
> [693354.105772] ? do_page_fault+0x9b/0x270
> [693354.105779] ? prepare_exit_to_usermode+0xf9/0x1a0
> [693354.105784] ? enter_from_user_mode+0x30/0x30
> [693354.105793] entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> [693354.105875] Allocated by task 1453337:
> [693354.106001] kasan_kmalloc+0xa0/0xd0
> [693354.106006] kmem_cache_alloc_node_trace+0x108/0x220
> [693354.106010] bfq_pd_alloc+0x96/0x120
> [693354.106015] blkcg_activate_policy+0x1b7/0x2b0
> [693354.106020] bfq_create_group_hierarchy+0x1e/0x80
> [693354.106026] bfq_init_queue+0x678/0x8c0
> [693354.106031] blk_mq_init_sched+0x1f8/0x460
> [693354.106037] elevator_switch_mq+0xe1/0x240
> [693354.106041] elevator_switch+0x25/0x40
> [693354.106045] elv_iosched_store+0x1a1/0x230
> [693354.106049] queue_attr_store+0x78/0xb0
> [693354.106053] kernfs_fop_write+0x1ab/0x280
> [693354.106056] vfs_write+0xe7/0x230
> [693354.106060] ksys_write+0xb0/0x140
> [693354.106064] do_syscall_64+0x112/0x370
> [693354.106069] entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> [693354.106114] Freed by task 1453336:
> [693354.106225] __kasan_slab_free+0x130/0x180
> [693354.106229] kfree+0x90/0x1b0
> [693354.106233] blkcg_deactivate_policy+0x12c/0x220
> [693354.106238] bfq_exit_queue+0xf5/0x110
> [693354.106241] blk_mq_exit_sched+0x104/0x130
> [693354.106245] __elevator_exit+0x45/0x60
> [693354.106249] elevator_switch_mq+0xd6/0x240
> [693354.106253] elevator_switch+0x25/0x40
> [693354.106257] elv_iosched_store+0x1a1/0x230
> [693354.106261] queue_attr_store+0x78/0xb0
> [693354.106264] kernfs_fop_write+0x1ab/0x280
> [693354.106268] vfs_write+0xe7/0x230
> [693354.106271] ksys_write+0xb0/0x140
> [693354.106275] do_syscall_64+0x112/0x370
> [693354.106280] entry_SYSCALL_64_after_hwframe+0x65/0xca
>
> [693354.106329] The buggy address belongs to the object at ffff888be0a35580
> which belongs to the cache kmalloc-1k of size 1024
> [693354.106736] The buggy address is located 228 bytes inside of
> 1024-byte region [ffff888be0a35580, ffff888be0a35980)
> [693354.107114] The buggy address belongs to the page:
> [693354.107273] page:ffffea002f828c00 count:1 mapcount:0 mapping:ffff888107c17080 index:0x0 compound_mapcount: 0
> [693354.107606] flags: 0x17ffffc0008100(slab|head)
> [693354.107760] raw: 0017ffffc0008100 ffffea002fcbc808 ffffea0030bd3a08 ffff888107c17080
> [693354.108020] raw: 0000000000000000 00000000001c001c 00000001ffffffff 0000000000000000
> [693354.108278] page dumped because: kasan: bad access detected
>
> [693354.108511] Memory state around the buggy address:
> [693354.108671] ffff888be0a35500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> [693354.116396] ffff888be0a35580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [693354.124473] >ffff888be0a35600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [693354.132421] ^
> [693354.140284] ffff888be0a35680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [693354.147912] ffff888be0a35700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [693354.155281] ==================================================================
>
> Freeing bfqg is protected by queue lock in blkcg_deactivate_policy(),
> but getting/using bfqg is protected by blkcg lock in
> bfq_io_set_weight_legacy(). If bfq_io_set_weight_legacy() get bfqg
> before freeing bfqg and use bfqg in the after, the use-after-free
> will occur.
>
> CPU0 CPU1
> blkcg_deactivate_policy
> spin_lock_irq(&q->queue_lock)
> bfq_io_set_weight_legacy
> spin_lock_irq(&blkcg->lock)
> blkg_to_bfqg(blkg)
> pd_to_bfqg(blkg->pd[pol->plid])
> ^^^^^^blkg->pd[pol->plid] != NULL
> bfqg != NULL
> pol->pd_free_fn(blkg->pd[pol->plid])
> pd_to_bfqg(blkg->pd[pol->plid])
> bfqg_put(bfqg)
> kfree(bfqg)
> blkg->pd[pol->plid] = NULL
> spin_unlock_irq(q->queue_lock);
> bfq_group_set_weight(bfqg, val, 0)
> bfqg->entity.new_weight
> ^^^^^^trigger uaf here
> spin_unlock_irq(&blkcg->lock);
>
> To fix this use-after-free, instead of holding blkcg->lock while
> walking ->blkg_list and getting/using bfqg, RCU walk ->blkg_list and
> hold the blkg's queue lock while getting/using bfqg.
>
> Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
> Signed-off-by: Li Jinlin <lijinlin3@xxxxxxxxxx>
> ---
> block/bfq-cgroup.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index e2f14508f2d6..7209060caa90 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -1025,21 +1025,25 @@ static int bfq_io_set_weight_legacy(struct cgroup_subsys_state *css,
> struct blkcg *blkcg = css_to_blkcg(css);
> struct bfq_group_data *bfqgd = blkcg_to_bfqgd(blkcg);
> struct blkcg_gq *blkg;
> + struct bfq_group *bfqg;
> int ret = -ERANGE;
>
> if (val < BFQ_MIN_WEIGHT || val > BFQ_MAX_WEIGHT)
> return ret;
>
> ret = 0;
> - spin_lock_irq(&blkcg->lock);
> bfqgd->weight = (unsigned short)val;
> - hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
> - struct bfq_group *bfqg = blkg_to_bfqg(blkg);
> +
> + rcu_read_lock();
> + hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
> + spin_lock_irq(&blkg->q->queue_lock);
> + bfqg = blkg_to_bfqg(blkg);
>
> if (bfqg)
> bfq_group_set_weight(bfqg, val, 0);
> + spin_unlock_irq(&blkg->q->queue_lock);
> }
> - spin_unlock_irq(&blkcg->lock);
> + rcu_read_unlock();
>
> return ret;
> }
Ping Paolo.
--
Jens Axboe
