Date:   Thu, 7 Jul 2022 14:26:22 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     syzbot <syzbot+49950ba66096b1f0209b@...kaller.appspotmail.com>,
        axboe@...nel.dk, gregkh@...uxfoundation.org, jirislaby@...nel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in pty_close

On 7/7/22 10:52, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    cb71b93c2dc3 Add linux-next specific files for 20220628
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14be3e84080000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=badbc1adb2d582eb
> dashboard link: https://syzkaller.appspot.com/bug?extid=49950ba66096b1f0209b
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=116d8ff4080000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13993e97f00000
> 
> The issue was bisected to:
> 
> commit a18427bb2d9b2c8bbacccd4f862b7b6b0a83ab75
> Author: Pavel Begunkov <asml.silence@...il.com>
> Date:   Thu Jun 23 13:24:49 2022 +0000
> 
>      io_uring: optimise submission side poll_refs

#syz test: git@...hub.com:isilence/linux.git poll-syz

> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1025755c080000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=1225755c080000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1425755c080000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+49950ba66096b1f0209b@...kaller.appspotmail.com
> Fixes: a18427bb2d9b ("io_uring: optimise submission side poll_refs")
> 
> ==================================================================
> 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:
>   <TASK>
>   __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
>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 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
>   </TASK>
> 
> 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
>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> 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
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

-- 
Pavel Begunkov

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