Re: [PATCH -next] block: fix uaf for flush rq while iterating tags

[Ming Lei <ming.lei@redhat.com>]

On Tue, Nov 05, 2024 at 03:36:36PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2024/11/05 15:18, Ming Lei 写道:
> > On Mon, Nov 04, 2024 at 07:00:05PM +0800, Yu Kuai wrote:
> > > From: Yu Kuai <yukuai3@huawei.com>
> > > 
> > > blk_mq_clear_flush_rq_mapping() is not called during scsi probe, by
> > > checking blk_queue_init_done(). However, QUEUE_FLAG_INIT_DONE is cleared
> > > in del_gendisk by commit aec89dc5d421 ("block: keep q_usage_counter in
> > > atomic mode after del_gendisk"), hence for disk like scsi, following
> > > blk_mq_destroy_queue() will not clear flush rq from tags->rqs[] as well,
> > > cause following uaf that is found by our syzkaller for v6.6:
> > > 
> > > ==================================================================
> > > BUG: KASAN: slab-use-after-free in blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261
> > > Read of size 4 at addr ffff88811c969c20 by task kworker/1:2H/224909
> > > 
> > > CPU: 1 PID: 224909 Comm: kworker/1:2H Not tainted 6.6.0-ga836a5060850 #32
> > > Workqueue: kblockd blk_mq_timeout_work
> > > Call Trace:
> > > 
> > > __dump_stack lib/dump_stack.c:88 [inline]
> > > dump_stack_lvl+0x91/0xf0 lib/dump_stack.c:106
> > > print_address_description.constprop.0+0x66/0x300 mm/kasan/report.c:364
> > > print_report+0x3e/0x70 mm/kasan/report.c:475
> > > kasan_report+0xb8/0xf0 mm/kasan/report.c:588
> > > blk_mq_find_and_get_req+0x16e/0x1a0 block/blk-mq-tag.c:261
> > > bt_iter block/blk-mq-tag.c:288 [inline]
> > > __sbitmap_for_each_set include/linux/sbitmap.h:295 [inline]
> > > sbitmap_for_each_set include/linux/sbitmap.h:316 [inline]
> > > bt_for_each+0x455/0x790 block/blk-mq-tag.c:325
> > > blk_mq_queue_tag_busy_iter+0x320/0x740 block/blk-mq-tag.c:534
> > > blk_mq_timeout_work+0x1a3/0x7b0 block/blk-mq.c:1673
> > > process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631
> > > process_scheduled_works kernel/workqueue.c:2704 [inline]
> > > worker_thread+0x804/0xe40 kernel/workqueue.c:2785
> > > kthread+0x346/0x450 kernel/kthread.c:388
> > > ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
> > > ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293
> > > 
> > > Allocated by task 942:
> > > kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
> > > kasan_set_track+0x25/0x30 mm/kasan/common.c:52
> > > ____kasan_kmalloc mm/kasan/common.c:374 [inline]
> > > __kasan_kmalloc mm/kasan/common.c:383 [inline]
> > > __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:380
> > > kasan_kmalloc include/linux/kasan.h:198 [inline]
> > > __do_kmalloc_node mm/slab_common.c:1007 [inline]
> > > __kmalloc_node+0x69/0x170 mm/slab_common.c:1014
> > > kmalloc_node include/linux/slab.h:620 [inline]
> > > kzalloc_node include/linux/slab.h:732 [inline]
> > > blk_alloc_flush_queue+0x144/0x2f0 block/blk-flush.c:499
> > > blk_mq_alloc_hctx+0x601/0x940 block/blk-mq.c:3788
> > > blk_mq_alloc_and_init_hctx+0x27f/0x330 block/blk-mq.c:4261
> > > blk_mq_realloc_hw_ctxs+0x488/0x5e0 block/blk-mq.c:4294
> > > blk_mq_init_allocated_queue+0x188/0x860 block/blk-mq.c:4350
> > > blk_mq_init_queue_data block/blk-mq.c:4166 [inline]
> > > blk_mq_init_queue+0x8d/0x100 block/blk-mq.c:4176
> > > scsi_alloc_sdev+0x843/0xd50 drivers/scsi/scsi_scan.c:335
> > > scsi_probe_and_add_lun+0x77c/0xde0 drivers/scsi/scsi_scan.c:1189
> > > __scsi_scan_target+0x1fc/0x5a0 drivers/scsi/scsi_scan.c:1727
> > > scsi_scan_channel drivers/scsi/scsi_scan.c:1815 [inline]
> > > scsi_scan_channel+0x14b/0x1e0 drivers/scsi/scsi_scan.c:1791
> > > scsi_scan_host_selected+0x2fe/0x400 drivers/scsi/scsi_scan.c:1844
> > > scsi_scan+0x3a0/0x3f0 drivers/scsi/scsi_sysfs.c:151
> > > store_scan+0x2a/0x60 drivers/scsi/scsi_sysfs.c:191
> > > dev_attr_store+0x5c/0x90 drivers/base/core.c:2388
> > > sysfs_kf_write+0x11c/0x170 fs/sysfs/file.c:136
> > > kernfs_fop_write_iter+0x3fc/0x610 fs/kernfs/file.c:338
> > > call_write_iter include/linux/fs.h:2083 [inline]
> > > new_sync_write+0x1b4/0x2d0 fs/read_write.c:493
> > > vfs_write+0x76c/0xb00 fs/read_write.c:586
> > > ksys_write+0x127/0x250 fs/read_write.c:639
> > > do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> > > do_syscall_64+0x70/0x120 arch/x86/entry/common.c:81
> > > entry_SYSCALL_64_after_hwframe+0x78/0xe2
> > > 
> > > Freed by task 244687:
> > > kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
> > > kasan_set_track+0x25/0x30 mm/kasan/common.c:52
> > > kasan_save_free_info+0x2b/0x50 mm/kasan/generic.c:522
> > > ____kasan_slab_free mm/kasan/common.c:236 [inline]
> > > __kasan_slab_free+0x12a/0x1b0 mm/kasan/common.c:244
> > > kasan_slab_free include/linux/kasan.h:164 [inline]
> > > slab_free_hook mm/slub.c:1815 [inline]
> > > slab_free_freelist_hook mm/slub.c:1841 [inline]
> > > slab_free mm/slub.c:3807 [inline]
> > > __kmem_cache_free+0xe4/0x520 mm/slub.c:3820
> > > blk_free_flush_queue+0x40/0x60 block/blk-flush.c:520
> > > blk_mq_hw_sysfs_release+0x4a/0x170 block/blk-mq-sysfs.c:37
> > > kobject_cleanup+0x136/0x410 lib/kobject.c:689
> > > kobject_release lib/kobject.c:720 [inline]
> > > kref_put include/linux/kref.h:65 [inline]
> > > kobject_put+0x119/0x140 lib/kobject.c:737
> > > blk_mq_release+0x24f/0x3f0 block/blk-mq.c:4144
> > > blk_free_queue block/blk-core.c:298 [inline]
> > > blk_put_queue+0xe2/0x180 block/blk-core.c:314
> > > blkg_free_workfn+0x376/0x6e0 block/blk-cgroup.c:144
> > > process_one_work+0x7c4/0x1450 kernel/workqueue.c:2631
> > > process_scheduled_works kernel/workqueue.c:2704 [inline]
> > > worker_thread+0x804/0xe40 kernel/workqueue.c:2785
> > > kthread+0x346/0x450 kernel/kthread.c:388
> > > ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
> > > ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:293
> > > 
> > > Other than blk_mq_clear_flush_rq_mapping(), the flag is only used in
> > > blk_register_queue() from initialization path, hence it's safe not to
> > > clear the flag in del_gendisk. And since QUEUE_FLAG_REGISTERED already
> > > make sure that queue should only be registered once, there is no need
> > > to test the flag as well.
> > 
> > But disk can be added again in case of sd rebind, so the check should be
> > kept.
> 
> I don't understand yet, I mean the other flag QUEUE_FLAG_REGISTERED can
> cover the case to call percpu_ref_switch_to_percpu() for the rebind
> case, the flag QUEUE_FLAG_INIT_DONE now is useless other than
> blk_mq_clear_flush_rq_mapping().

OK, looks fine, since queue usage counter only works in percpu mode with
disk attached for !GD_OWNS_QUEUE, maybe QUEUE_FLAG_INIT_DONE can be renamed
too, but anyway:

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming