KASAN: use-after-free Read in pty_close

Status: fixed on 2023/02/24 13:51
Subsystems: serial io-uring fuse
[Documentation on labels]
Fix commit: 7a121ced6e64 io_uring: don't miss setting REQ_F_DOUBLE_POLL
First crash: 683d, last: 656d
Cause bisection: introduced by (bisect log) :
commit a18427bb2d9b2c8bbacccd4f862b7b6b0a83ab75
Author: Pavel Begunkov <>
Date: Thu Jun 23 13:24:49 2022 +0000

  io_uring: optimise submission side poll_refs

Crash: KASAN: use-after-free Read in pty_close (log)
Repro: C syz .config
Discussions (2)
Title Replies (including bot) Last reply
[PATCH for-next 0/4] poll locking fixes 6 (6) 2022/07/07 23:27
[syzbot] KASAN: use-after-free Read in pty_close 2 (5) 2022/07/07 13:57
Last patch testing requests (2)
Created Duration User Patch Repo Result
2022/07/07 13:37 18m poll-syz OK log
2022/07/07 13:26 0m poll-syz error OK

Sample crash report:
BUG: KASAN: use-after-free in __wake_up_common+0x637/0x650 kernel/sched/wait.c:100
Read of size 8 at addr ffff8880253cdfb0 by task syz-executor106/3800

CPU: 0 PID: 3800 Comm: syz-executor106 Not tainted 5.19.0-rc4-next-20220628-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/29/2022
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
 kasan_report+0xbe/0x1f0 mm/kasan/report.c:495
 __wake_up_common+0x637/0x650 kernel/sched/wait.c:100
 __wake_up_common_lock+0xd0/0x130 kernel/sched/wait.c:137
 pty_close+0x224/0x4f0 drivers/tty/pty.c:68
 tty_release+0x45e/0x1200 drivers/tty/tty_io.c:1758
 __fput+0x277/0x9d0 fs/file_table.c:317
 task_work_run+0xdd/0x1a0 kernel/task_work.c:177
 ptrace_notify+0x114/0x140 kernel/signal.c:2353
 ptrace_report_syscall include/linux/ptrace.h:420 [inline]
 ptrace_report_syscall_exit include/linux/ptrace.h:482 [inline]
 syscall_exit_work kernel/entry/common.c:249 [inline]
 syscall_exit_to_user_mode_prepare+0x129/0x280 kernel/entry/common.c:276
 __syscall_exit_to_user_mode_work kernel/entry/common.c:281 [inline]
 syscall_exit_to_user_mode+0x9/0x50 kernel/entry/common.c:294
 do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
RIP: 0033:0x7f4caf4b25d9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f4caf45f268 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: 0000000000006a00 RBX: 00007f4caf5394e0 RCX: 00007f4caf4b25d9
RDX: 000000000000ff2e RSI: 0000000020000080 RDI: 0000000000000007
RBP: 00007f4caf506074 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f4caf5394e8
R13: 0000000020004400 R14: 6d74702f7665642f R15: 0000000000000006

Allocated by task 3801:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:436 [inline]
 ____kasan_kmalloc mm/kasan/common.c:515 [inline]
 ____kasan_kmalloc mm/kasan/common.c:474 [inline]
 __kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:524
 kmalloc include/linux/slab.h:600 [inline]
 __io_queue_proc+0x2dc/0x950 io_uring/poll.c:429
 poll_wait include/linux/poll.h:49 [inline]
 n_tty_poll+0xb4/0x8a0 drivers/tty/n_tty.c:2425
 tty_poll+0x139/0x1b0 drivers/tty/tty_io.c:2212
 vfs_poll include/linux/poll.h:88 [inline]
 __io_arm_poll_handler+0x488/0x1060 io_uring/poll.c:511
 io_arm_poll_handler+0x5c6/0xce0 io_uring/poll.c:638
 io_queue_async+0xc1/0x3e0 io_uring/io_uring.c:1753
 io_queue_sqe io_uring/io_uring.c:1787 [inline]
 io_submit_sqe io_uring/io_uring.c:2036 [inline]
 io_submit_sqes+0x15fc/0x1ec0 io_uring/io_uring.c:2147
 __do_sys_io_uring_enter+0xb85/0x1eb0 io_uring/io_uring.c:3087
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80

Freed by task 3803:
 kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38
 kasan_set_track+0x21/0x30 mm/kasan/common.c:45
 kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
 ____kasan_slab_free mm/kasan/common.c:366 [inline]
 ____kasan_slab_free+0x166/0x1c0 mm/kasan/common.c:328
 kasan_slab_free include/linux/kasan.h:200 [inline]
 slab_free_hook mm/slub.c:1754 [inline]
 slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1780
 slab_free mm/slub.c:3534 [inline]
 kfree+0xe2/0x4d0 mm/slub.c:4562
 io_clean_op+0x1b1/0xa40 io_uring/io_uring.c:1555
 io_dismantle_req io_uring/io_uring.c:930 [inline]
 io_free_req+0xc9/0x299 io_uring/io_uring.c:940
 io_put_req_find_next io_uring/io_uring.c:1236 [inline]
 io_wq_free_work.cold+0x62/0x67 io_uring/io_uring.c:1636
 io_worker_handle_work+0xc48/0x1c60 io_uring/io-wq.c:590
 io_wqe_worker+0x640/0xe90 io_uring/io-wq.c:634
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302

The buggy address belongs to the object at ffff8880253cdf80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 48 bytes inside of
 64-byte region [ffff8880253cdf80, ffff8880253cdfc0)

The buggy address belongs to the physical page:
page:ffffea000094f340 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x253cd
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 ffffea0000963c00 dead000000000003 ffff888011841640
raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 11, tgid 11 (kworker/u4:1), ts 9976176866, free_ts 0
 prep_new_page mm/page_alloc.c:2535 [inline]
 get_page_from_freelist+0x210d/0x3a30 mm/page_alloc.c:4282
 __alloc_pages+0x1c7/0x510 mm/page_alloc.c:5506
 alloc_pages+0x1aa/0x310 mm/mempolicy.c:2280
 alloc_slab_page mm/slub.c:1824 [inline]
 allocate_slab+0x27e/0x3d0 mm/slub.c:1969
 new_slab mm/slub.c:2029 [inline]
 ___slab_alloc+0x89d/0xef0 mm/slub.c:3031
 __slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3118
 slab_alloc_node mm/slub.c:3209 [inline]
 slab_alloc mm/slub.c:3251 [inline]
 __kmalloc+0x3a2/0x450 mm/slub.c:4420
 kmalloc include/linux/slab.h:605 [inline]
 kzalloc include/linux/slab.h:733 [inline]
 lsm_task_alloc security/security.c:615 [inline]
 security_task_alloc+0x10b/0x250 security/security.c:1655
 copy_process+0x23e0/0x7080 kernel/fork.c:2219
 kernel_clone+0xe7/0xab0 kernel/fork.c:2652
 user_mode_thread+0xad/0xe0 kernel/fork.c:2721
 call_usermodehelper_exec_work kernel/umh.c:174 [inline]
 call_usermodehelper_exec_work+0xcc/0x180 kernel/umh.c:160
 process_one_work+0x991/0x1610 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e9/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8880253cde80: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff8880253cdf00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8880253cdf80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff8880253ce000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880253ce080: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2022/07/07 04:16 linux-next cb71b93c2dc3 bff65f44 .config strace log report syz C ci-upstream-linux-next-kasan-gce-root KASAN: use-after-free Read in pty_close
2022/08/03 18:18 linux-next cb71b93c2dc3 1c9013ac .config console log report info ci-upstream-linux-next-kasan-gce-root KASAN: use-after-free Read in pty_close
2022/07/21 17:21 linux-next cb71b93c2dc3 6e67af9d .config console log report info ci-upstream-linux-next-kasan-gce-root KASAN: use-after-free Read in pty_close
2022/07/20 18:03 linux-next cb71b93c2dc3 775344bc .config console log report info ci-upstream-linux-next-kasan-gce-root KASAN: use-after-free Read in pty_close
* Struck through repros no longer work on HEAD.