Re: WARNING in bpf_cgroup_link_release

[Daniel Borkmann <daniel@iogearbox.net>]

On 4/15/20 8:55 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:

Andrii, ptal.

> HEAD commit:    1a323ea5 x86: get rid of 'errret' argument to __get_user_x..
> git tree:       bpf-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=148ccb57e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8c1e98458335a7d1
> dashboard link: https://syzkaller.appspot.com/bug?extid=8a5dadc5c0b1d7055945
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8a5dadc5c0b1d7055945@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 25081 at kernel/bpf/cgroup.c:796 bpf_cgroup_link_release+0x260/0x3a0 kernel/bpf/cgroup.c:796
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 25081 Comm: syz-executor.1 Not tainted 5.6.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x188/0x20d lib/dump_stack.c:118
>   panic+0x2e3/0x75c kernel/panic.c:221
>   __warn.cold+0x2f/0x35 kernel/panic.c:582
>   report_bug+0x27b/0x2f0 lib/bug.c:195
>   fixup_bug arch/x86/kernel/traps.c:175 [inline]
>   fixup_bug arch/x86/kernel/traps.c:170 [inline]
>   do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267
>   do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
>   invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
> RIP: 0010:bpf_cgroup_link_release+0x260/0x3a0 kernel/bpf/cgroup.c:796
> Code: cf ff 5b 5d 41 5c e9 df 2a e9 ff e8 da 2a e9 ff 48 c7 c7 20 f4 9d 89 e8 de a0 3a 06 5b 5d 41 5c e9 c5 2a e9 ff e8 c0 2a e9 ff <0f> 0b e9 57 fe ff ff e8 a4 3d 26 00 e9 2a fe ff ff e8 9a 3d 26 00
> RSP: 0018:ffffc900019a7dc0 EFLAGS: 00010246
> RAX: 0000000000040000 RBX: ffff88808c3eac00 RCX: ffffc9000415a000
> RDX: 0000000000040000 RSI: ffffffff8189bea0 RDI: 0000000000000005
> RBP: 00000000fffffff4 R08: ffff88809055e000 R09: ffffed1015cc70f4
> R10: ffffed1015cc70f3 R11: ffff8880ae63879b R12: ffff88808c3eac60
> R13: ffff88808c3eac10 R14: ffffc90000f32000 R15: ffffffff817f8e60
>   bpf_link_free+0x80/0x140 kernel/bpf/syscall.c:2217
>   bpf_link_put+0x15e/0x1b0 kernel/bpf/syscall.c:2243
>   bpf_link_release+0x33/0x40 kernel/bpf/syscall.c:2251
>   __fput+0x2e9/0x860 fs/file_table.c:280
>   task_work_run+0xf4/0x1b0 kernel/task_work.c:123
>   tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>   exit_to_usermode_loop+0x2fa/0x360 arch/x86/entry/common.c:165
>   prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
>   do_syscall_64+0x6b1/0x7d0 arch/x86/entry/common.c:305
>   entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x45c889
> Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fddaf43fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 00007fddaf4406d4 RCX: 000000000045c889
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
> RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000006
> R13: 0000000000000078 R14: 00000000005043d2 R15: 0000000000000000
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
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