Re: BUG: unable to handle kernel paging request in refcount_inc_not_zero_checked

[Paolo Bonzini]

On 10/10/2018 09:57, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:ÂÂÂ 570b7bdeaf18 Add linux-next specific files for 20181009
> git tree:ÂÂÂÂÂÂ linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15f27959400000
> kernel config:Â https://syzkaller.appspot.com/x/.config?x=9b5a60e1381390c4
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=e593df3bb8f541d497b9
> compiler:ÂÂÂÂÂÂ gcc (GCC) 8.0.1 20180413 (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+e593df3bb8f541d497b9@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BUG: unable to handle kernel paging request at ffffc90001b356b0
> PGD 1da948067 P4D 1da948067 PUD 1da949067 PMD 1ce844067 PTE 0
> Oops: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 11542 Comm: syz-executor2 Not tainted
> 4.19.0-rc7-next-20181009+ #90
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> kobject: 'queues' (00000000da0a0759): kobject_uevent_env
> RIP: 0010:__read_once_size include/linux/compiler.h:179 [inline]
> RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:31 [inline]
> RIP: 0010:atomic_read include/asm-generic/atomic-instrumented.h:22 [inline]
> RIP: 0010:refcount_inc_not_zero_checked+0xbb/0x2f0 lib/refcount.c:120
> Code: e7 e8 89 4b 30 fe 4c 89 e0 48 c1 e8 03 0f b6 14 18 4c 89 e0 83 e0
> 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 0b 02 00 00 49 8d 5d c0 <45> 8b 3c
> 24 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 0f
> kobject: 'queues' (00000000da0a0759): kobject_uevent_env: filter
> function caused the event to drop!
> RSP: 0018:ffff88017cf9f618 EFLAGS: 00010246
> RAX: 0000000000000003 RBX: ffff88017cf9f690 RCX: ffffffff83929317
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffc90001b356b0
> RBP: ffff88017cf9f6f8 R08: fffff52000366ad7 R09: fffff52000366ad6
> R10: fffff52000366ad6 R11: ffffc90001b356b3 R12: ffffc90001b356b0
> R13: ffff88017cf9f6d0 R14: ffffffff892b6d60 R15: ffff8801d4803400
> FS:Â 00007fb683cfa700(0000) GS:ffff8801daf00000(0000)
> knlGS:0000000000000000
> CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> kobject: 'loop1' (00000000bc5d5992): kobject_uevent_env
> CR2: ffffc90001b356b0 CR3: 00000001d2369000 CR4: 00000000001426e0
> netlink: 72 bytes leftover after parsing attributes in process
> `syz-executor3'.
> Call Trace:
> Ârefcount_inc_checked+0x15/0x70 lib/refcount.c:153
> kobject: 'loop1' (00000000bc5d5992): fill_kobj_path: path =
> '/devices/virtual/block/loop1'
> Âkvm_get_kvm arch/x86/kvm/../../../virt/kvm/kvm_main.c:765 [inline]
> Âkvm_ioctl_create_device arch/x86/kvm/../../../virt/kvm/kvm_main.c:2923
> [inline]
> Âkvm_vm_ioctl+0xedf/0x1d60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3113
> Âvfs_ioctl fs/ioctl.c:46 [inline]
> Âfile_ioctl fs/ioctl.c:501 [inline]
> Âdo_vfs_ioctl+0x1de/0x1720 fs/ioctl.c:685
> Âksys_ioctl+0xa9/0xd0 fs/ioctl.c:702
> Â__do_sys_ioctl fs/ioctl.c:709 [inline]
> Â__se_sys_ioctl fs/ioctl.c:707 [inline]
> Â__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:707
> Âdo_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> Âentry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457579
> Code: 1d b4 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 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fb683cf9c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457579
> RDX: 00000000200002c0 RSI: 00000000c00caee0 RDI: 0000000000000008
> RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb683cfa6d4
> R13: 00000000004bfbd1 R14: 00000000004cfc58 R15: 00000000ffffffff
> Modules linked in:
> CR2: ffffc90001b356b0
> ---[ end trace 6ee8acb8091e879f ]---
> RIP: 0010:__read_once_size include/linux/compiler.h:179 [inline]
> RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:31 [inline]
> RIP: 0010:atomic_read include/asm-generic/atomic-instrumented.h:22 [inline]
> RIP: 0010:refcount_inc_not_zero_checked+0xbb/0x2f0 lib/refcount.c:120
> Code: e7 e8 89 4b 30 fe 4c 89 e0 48 c1 e8 03 0f b6 14 18 4c 89 e0 83 e0
> 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 0b 02 00 00 49 8d 5d c0 <45> 8b 3c
> 24 48 b8 00 00 00 00 00 fc ff df 48 89 da 48 c1 ea 03 0f
> RSP: 0018:ffff88017cf9f618 EFLAGS: 00010246
> RAX: 0000000000000003 RBX: ffff88017cf9f690 RCX: ffffffff83929317
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffc90001b356b0
> RBP: ffff88017cf9f6f8 R08: fffff52000366ad7 R09: fffff52000366ad6
> R10: fffff52000366ad6 R11: ffffc90001b356b3 R12: ffffc90001b356b0
> R13: ffff88017cf9f6d0 R14: ffffffff892b6d60 R15: ffff8801d4803400
> FS:Â 00007fb683cfa700(0000) GS:ffff8801daf00000(0000)
> knlGS:0000000000000000
> CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffc90001b356b0 CR3: 00000001d2369000 CR4: 00000000001426e0
> 
> 
> ---
> This bug 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@xxxxxxxxxxxxxxxxx
> 
> syzbot will keep track of this bug report. See:
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> syzbot.
> 

#syz dup: WARNING: refcount bug in kvm_vm_ioctl