Re: [syzbot] WARNING: refcount bug in mm_update_next_owner

[Jann Horn]

All 5 console logs listed on the syzkaller dashboard for this one have
io-uring with IORING_OP_POLL_ADD somewhere. Could that be related?

On Mon, Jan 16, 2023 at 8:31 AM syzbot
<syzbot+1d4c86ac0fed92e3fc78@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    0a093b2893c7 Add linux-next specific files for 20230112
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a8e102480000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=835f3591019836d5
> dashboard link: https://syzkaller.appspot.com/bug?extid=1d4c86ac0fed92e3fc78
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/8111a570d6cb/disk-0a093b28.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/ecc135b7fc9a/vmlinux-0a093b28.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ca8d73b446ea/bzImage-0a093b28.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+1d4c86ac0fed92e3fc78@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 0 PID: 5316 at lib/refcount.c:25 refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
> Modules linked in:
> CPU: 0 PID: 5316 Comm: syz-executor.4 Not tainted 6.2.0-rc3-next-20230112-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:refcount_warn_saturate+0x17c/0x1f0 lib/refcount.c:25
> Code: 0a 31 ff 89 de e8 d4 13 78 fd 84 db 0f 85 2e ff ff ff e8 57 17 78 fd 48 c7 c7 60 87 a6 8a c6 05 e0 ce 54 0a 01 e8 98 a7 b2 05 <0f> 0b e9 0f ff ff ff e8 38 17 78 fd 0f b6 1d ca ce 54 0a 31 ff 89
> RSP: 0018:ffffc90005967d80 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff8880829f3a80 RSI: ffffffff8166972c RDI: fffff52000b2cfa2
> RBP: ffff888082ae3aa8 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000000 R12: ffff88807e520900
> R13: ffff888082ae3fa8 R14: 0000000000000000 R15: ffff888082ae3aa8
> FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b32f23000 CR3: 000000007716c000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __refcount_add include/linux/refcount.h:199 [inline]
>  __refcount_inc include/linux/refcount.h:250 [inline]
>  refcount_inc include/linux/refcount.h:267 [inline]
>  get_task_struct include/linux/sched/task.h:110 [inline]
>  mm_update_next_owner+0x585/0x7b0 kernel/exit.c:504
>  exit_mm kernel/exit.c:562 [inline]
>  do_exit+0x9a4/0x2a90 kernel/exit.c:854
>  do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
>  __do_sys_exit_group kernel/exit.c:1023 [inline]
>  __se_sys_exit_group kernel/exit.c:1021 [inline]
>  __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1021
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f51f5a8c0c9
> Code: Unable to access opcode bytes at 0x7f51f5a8c09f.
> RSP: 002b:00007ffe3c730ad8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 000000000000001e RCX: 00007f51f5a8c0c9
> RDX: 00007f51f5a3df7b RSI: ffffffffffffffb8 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 000000002ed3101e R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 0000000000000000 R14: 0000000000000001 R15: 00007ffe3c730bc0
>  </TASK>
>
>
> ---
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>
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