Re: KASAN: use-after-free Read in idr_for_each (2)

[Pavel Begunkov <asml.silence@gmail.com>]

On 18/12/2020 16:44, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> KASAN: use-after-free Read in idr_for_each

#syz test: git://git.kernel.dk/linux-block io_uring-5.12

> 
> ==================================================================
> BUG: KASAN: use-after-free in radix_tree_next_slot include/linux/radix-tree.h:422 [inline]
> BUG: KASAN: use-after-free in idr_for_each+0x206/0x220 lib/idr.c:202
> Read of size 8 at addr ffff888042e76040 by task kworker/u4:5/3340
> 
> CPU: 0 PID: 3340 Comm: kworker/u4:5 Not tainted 5.10.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events_unbound io_ring_exit_work
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0xae/0x4c8 mm/kasan/report.c:385
>  __kasan_report mm/kasan/report.c:545 [inline]
>  kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
>  radix_tree_next_slot include/linux/radix-tree.h:422 [inline]
>  idr_for_each+0x206/0x220 lib/idr.c:202
>  io_destroy_buffers fs/io_uring.c:8541 [inline]
>  io_ring_ctx_free fs/io_uring.c:8564 [inline]
>  io_ring_exit_work+0x394/0x730 fs/io_uring.c:8639
>  process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>  kthread+0x3b1/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> 
> Allocated by task 28625:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track mm/kasan/common.c:56 [inline]
>  __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:461
>  slab_post_alloc_hook mm/slab.h:512 [inline]
>  slab_alloc_node mm/slub.c:2889 [inline]
>  slab_alloc mm/slub.c:2897 [inline]
>  kmem_cache_alloc+0x145/0x350 mm/slub.c:2902
>  radix_tree_node_alloc.constprop.0+0x7c/0x350 lib/radix-tree.c:274
>  idr_get_free+0x554/0xa60 lib/radix-tree.c:1504
>  idr_alloc_u32+0x170/0x2d0 lib/idr.c:46
>  idr_alloc+0xc2/0x130 lib/idr.c:87
>  io_provide_buffers fs/io_uring.c:4230 [inline]
>  io_issue_sqe+0x3681/0x44e0 fs/io_uring.c:6264
>  __io_queue_sqe+0x228/0x1120 fs/io_uring.c:6477
>  io_queue_sqe+0x631/0x10f0 fs/io_uring.c:6543
>  io_submit_sqe fs/io_uring.c:6616 [inline]
>  io_submit_sqes+0x135a/0x2530 fs/io_uring.c:6864
>  __do_sys_io_uring_enter+0x591/0x1c00 fs/io_uring.c:9174
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 8890:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:56
>  kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:352
>  __kasan_slab_free+0x102/0x140 mm/kasan/common.c:422
>  slab_free_hook mm/slub.c:1544 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1577
>  slab_free mm/slub.c:3140 [inline]
>  kmem_cache_free+0x82/0x360 mm/slub.c:3156
>  rcu_do_batch kernel/rcu/tree.c:2489 [inline]
>  rcu_core+0x75d/0xf80 kernel/rcu/tree.c:2723
>  __do_softirq+0x2bc/0xa77 kernel/softirq.c:343
> 
> Last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_record_aux_stack+0xc0/0xf0 mm/kasan/generic.c:343
>  __call_rcu kernel/rcu/tree.c:2965 [inline]
>  call_rcu+0xbb/0x710 kernel/rcu/tree.c:3038
>  radix_tree_node_free lib/radix-tree.c:308 [inline]
>  delete_node+0x591/0x8c0 lib/radix-tree.c:571
>  __radix_tree_delete+0x190/0x370 lib/radix-tree.c:1377
>  radix_tree_delete_item+0xe7/0x230 lib/radix-tree.c:1428
>  __io_remove_buffers fs/io_uring.c:4122 [inline]
>  __io_remove_buffers fs/io_uring.c:4101 [inline]
>  __io_destroy_buffers+0x161/0x200 fs/io_uring.c:8535
>  idr_for_each+0x113/0x220 lib/idr.c:208
>  io_destroy_buffers fs/io_uring.c:8541 [inline]
>  io_ring_ctx_free fs/io_uring.c:8564 [inline]
>  io_ring_exit_work+0x394/0x730 fs/io_uring.c:8639
>  process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
>  worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
>  kthread+0x3b1/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> 
> Second to last potentially related work creation:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>  kasan_record_aux_stack+0xc0/0xf0 mm/kasan/generic.c:343
>  __call_rcu kernel/rcu/tree.c:2965 [inline]
>  call_rcu+0xbb/0x710 kernel/rcu/tree.c:3038
>  xa_node_free lib/xarray.c:258 [inline]
>  xas_delete_node lib/xarray.c:494 [inline]
>  update_node lib/xarray.c:756 [inline]
>  xas_store+0xbeb/0x1c10 lib/xarray.c:841
>  __xa_erase lib/xarray.c:1489 [inline]
>  xa_erase+0xb0/0x170 lib/xarray.c:1510
>  io_uring_del_task_file fs/io_uring.c:8889 [inline]
>  __io_uring_files_cancel+0xdbf/0x1550 fs/io_uring.c:8925
>  io_uring_files_cancel include/linux/io_uring.h:51 [inline]
>  exit_files+0xe4/0x170 fs/file.c:431
>  do_exit+0xb4f/0x2a00 kernel/exit.c:818
>  do_group_exit+0x125/0x310 kernel/exit.c:920
>  get_signal+0x3e9/0x2160 kernel/signal.c:2770
>  arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:811
>  handle_signal_work kernel/entry/common.c:147 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
>  exit_to_user_mode_prepare+0x124/0x200 kernel/entry/common.c:201
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
>  syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:302
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff888042e76000
>  which belongs to the cache radix_tree_node of size 576
> The buggy address is located 64 bytes inside of
>  576-byte region [ffff888042e76000, ffff888042e76240)
> The buggy address belongs to the page:
> page:0000000090e8be83 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x42e76
> head:0000000090e8be83 order:1 compound_mapcount:0
> flags: 0xfff00000010200(slab|head)
> raw: 00fff00000010200 dead000000000100 dead000000000122 ffff88801084db40
> raw: ffff888042e76580 00000000800b000a 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff888042e75f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff888042e75f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff888042e76000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                            ^
>  ffff888042e76080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888042e76100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> Tested on:
> 
> commit:         dfea9fce io_uring: close a small race gap for files cancel
> git tree:       git://git.kernel.dk/linux-block
> console output: https://syzkaller.appspot.com/x/log.txt?x=1263a46b500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4db50a97037d9f3e
> dashboard link: https://syzkaller.appspot.com/bug?extid=12056a09a0311d758e60
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 

-- 
Pavel Begunkov