Re: general protection fault in __dentry_path

[Tetsuo Handa]

This report should be sent to KVM people.

I guess that a lack of serialization between kvm_create_vm_debugfs() from
kvm_dev_ioctl_create_vm() and kvm_destroy_vm_debugfs() from kvm_destroy_vm()
is causing a race on kvm->debugfs_dentry when kvm_uevent_notify_change()
called dentry_path_raw(kvm->debugfs_dentry).

On 2019/01/30 20:32, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:ÂÂÂ 02495e76ded5 Add linux-next specific files for 20190130
> git tree:ÂÂÂÂÂÂ linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=106161ef400000
> kernel config:Â https://syzkaller.appspot.com/x/.config?x=a2b2e9c0bc43c14d
> dashboard link: https://syzkaller.appspot.com/bug?extid=7857962b4d45e602b8ad
> compiler:ÂÂÂÂÂÂ gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:ÂÂÂÂÂ https://syzkaller.appspot.com/x/repro.syz?x=1182e5b8c00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+7857962b4d45e602b8ad@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 8239 Comm: syz-executor4 Not tainted 5.0.0-rc4-next-20190130 #22
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:__dentry_path+0x2a5/0xaa0 fs/d_path.c:344
> Code: 00 00 e8 1e 9d 9f ff 48 c7 c7 68 26 81 89 e8 72 c4 14 06 e8 0d 9d 9f ff 48 8b 85 00 ff ff ff 48 8d 78 40 48 89 f8 48 c1 e8 03 <42> 80 3c 38 00 0f 85 b0 07 00 00 48 8b 85 00 ff ff ff 4c 8b 68 40
> RSP: 0018:ffff88808ab5f8a8 EFLAGS: 00010207
> RAX: 0000000000000005 RBX: 0000000000000000 RCX: ffffffff81e27f21
> RDX: 0000000000000000 RSI: ffffffff81e27c43 RDI: 000000000000002f
> RBP: ffff88808ab5f9d0 R08: ffff88809edd4280 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff88808ab5f9a8
> R13: 0000000000000000 R14: 0000000000000c78 R15: dffffc0000000000
> FS:Â 00007f69a6d18700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000144a008 CR3: 00000000a1190000 CR4: 00000000001426f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> Âdentry_path_raw+0x26/0x30 fs/d_path.c:371
> Âkvm_uevent_notify_change.part.0+0x213/0x440 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4050
> Âkvm_uevent_notify_change arch/x86/kvm/../../../virt/kvm/kvm_main.c:4017 [inline]
> Âkvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3355 [inline]
> Âkvm_dev_ioctl+0x137a/0x1a60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3377
> Âvfs_ioctl fs/ioctl.c:46 [inline]
> Âfile_ioctl fs/ioctl.c:509 [inline]
> Âdo_vfs_ioctl+0x107b/0x17d0 fs/ioctl.c:696
> Âksys_ioctl+0xab/0xd0 fs/ioctl.c:713
> Â__do_sys_ioctl fs/ioctl.c:720 [inline]
> Â__se_sys_ioctl fs/ioctl.c:718 [inline]
> Â__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> Âdo_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
> Âentry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x458089
> Code: 6d b7 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 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f69a6d17c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458089
> RDX: 0000000000000000 RSI: 000000000000ae01 RDI: 0000000000000006
> RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f69a6d186d4
> R13: 00000000004c0bcf R14: 00000000004d2890 R15: 00000000ffffffff
> Modules linked in:
> ---[ end trace c2b508264c762aae ]---
> RIP: 0010:__dentry_path+0x2a5/0xaa0 fs/d_path.c:344
> Code: 00 00 e8 1e 9d 9f ff 48 c7 c7 68 26 81 89 e8 72 c4 14 06 e8 0d 9d 9f ff 48 8b 85 00 ff ff ff 48 8d 78 40 48 89 f8 48 c1 e8 03 <42> 80 3c 38 00 0f 85 b0 07 00 00 48 8b 85 00 ff ff ff 4c 8b 68 40
> RSP: 0018:ffff88808ab5f8a8 EFLAGS: 00010207
> RAX: 0000000000000005 RBX: 0000000000000000 RCX: ffffffff81e27f21
> RDX: 0000000000000000 RSI: ffffffff81e27c43 RDI: 000000000000002f
> RBP: ffff88808ab5f9d0 R08: ffff88809edd4280 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: ffff88808ab5f9a8
> R13: 0000000000000000 R14: 0000000000000c78 R15: dffffc0000000000
> FS:Â 00007f69a6d18700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fec12a1fdb8 CR3: 00000000a1190000 CR4: 00000000001426f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
>