Re: invalid opcode in close_fs_devices

From: Anand Jain
Date: Fri Nov 30 2018 - 01:00:28 EST



On 11/29/2018 03:33 PM, syzbot wrote:
Hello,

syzbot found the following crash on:

HEAD commit:ÂÂÂ ef78e5ec9214 ia64: export node_distance function
git tree:ÂÂÂÂÂÂ upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1514f733400000
kernel config:Â https://syzkaller.appspot.com/x/.config?x=c94f9f0c0363db4b
dashboard link: https://syzkaller.appspot.com/bug?extid=cabf977d00d3db1fdc37
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+cabf977d00d3db1fdc37@xxxxxxxxxxxxxxxxxxxxxxxxx

invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 6312 Comm: syz-executor4 Not tainted 4.20.0-rc4+ #132
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:btrfs_close_one_device fs/btrfs/volumes.c:1039 [inline]


1037 new_device = btrfs_alloc_device(NULL, &device->devid,
1038 device->uuid);
1039 BUG_ON(IS_ERR(new_device)); /* -ENOMEM */


As part of close operations (lets say for unmount). We alloc a new
struct btrfs_device, copy few items and free the original struct
btrfs_device. This comes from the original design, this approach
has been bothering me and few others. We don't know for sure what
is the motivation to design like this, but I guess to satisfy the
RCUs.

To fix- one idea is to selectively reset the struct btrfs_device
members, avoid allocating a new btrfS_device and thus no need to
fail the unmount due to ENOMEM here.

-Anand


RIP: 0010:close_fs_devices.part.44+0x7be/0xa20 fs/btrfs/volumes.c:1063
Code: 48 8d 7b 30 49 89 44 24 18 48 89 f8 48 c1 e8 03 42 80 3c 28 00 0f 85 bd 01 00 00 48 83 6b 30 01 e9 7a fa ff ff e8 82 85 8c fe <0f> 0b e8 7b 85 8c fe 0f 0b e8 74 85 8c fe 0f 0b e9 6f fd ff ff e8
RSP: 0018:ffff8881b7b771d8 EFLAGS: 00010212
RAX: 0000000000040000 RBX: ffff8881cdebb300 RCX: ffffc9000dea2000
RDX: 0000000000022db4 RSI: ffffffff82f3057e RDI: 0000000000000007
RBP: ffff8881b7b77380 R08: ffff8881b50d0000 R09: 0000000000000006
R10: 0000000000000000 R11: ffff8881b50d0000 R12: ffff8881bad2b200
R13: dffffc0000000000 R14: fffffffffffffff4 R15: 0000000000000000
FS:Â 00007fc6d31a2700(0000) GS:ffff8881dae00000(0000) knlGS:0000000000000000
CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000400200 CR3: 00000001d3b95000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
Âclose_fs_devices fs/btrfs/volumes.c:1095 [inline]
Âbtrfs_close_devices+0xa1/0x210 fs/btrfs/volumes.c:1081
Âbtrfs_mount_root+0x13d2/0x1d70 fs/btrfs/super.c:1619
Âmount_fs+0xae/0x31d fs/super.c:1261
Âvfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
Âvfs_kern_mount+0x40/0x60 fs/namespace.c:951
Âbtrfs_mount+0x4a3/0x2136 fs/btrfs/super.c:1670
Âmount_fs+0xae/0x31d fs/super.c:1261
Âvfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
Âvfs_kern_mount fs/namespace.c:951 [inline]
Âdo_new_mount fs/namespace.c:2469 [inline]
Âdo_mount+0x581/0x31f0 fs/namespace.c:2801
Âksys_mount+0x12d/0x140 fs/namespace.c:3017
Â__do_sys_mount fs/namespace.c:3031 [inline]
Â__se_sys_mount fs/namespace.c:3028 [inline]
Â__x64_sys_mount+0xbe/0x150 fs/namespace.c:3028
Âdo_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
Âentry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459fda
Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 7d 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 5a 89 fb ff c3 66 0f 1f 84 00 00 00 00 00
RSP: 002b:00007fc6d31a1a88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fc6d31a1b30 RCX: 0000000000459fda
RDX: 00007fc6d31a1ad0 RSI: 0000000020000740 RDI: 00007fc6d31a1af0
RBP: 0000000020000740 R08: 00007fc6d31a1b30 R09: 00007fc6d31a1ad0
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000004
R13: 0000000000000000 R14: 00000000004d8ef0 R15: 0000000000000003
Modules linked in:
kobject: 'loop1' (0000000014e46057): kobject_uevent_env
kobject: 'loop1' (0000000014e46057): fill_kobj_path: path = '/devices/virtual/block/loop1'
kobject: 'loop1' (0000000014e46057): kobject_uevent_env
kobject: 'loop1' (0000000014e46057): fill_kobj_path: path = '/devices/virtual/block/loop1'
kobject: 'loop1' (0000000014e46057): kobject_uevent_env
kobject: 'loop1' (0000000014e46057): fill_kobj_path: path = '/devices/virtual/block/loop1'
kobject: 'loop1' (0000000014e46057): kobject_uevent_env
kobject: 'loop1' (0000000014e46057): fill_kobj_path: path = '/devices/virtual/block/loop1'
---[ end trace 260d74aed8afc1e0 ]---
RIP: 0010:btrfs_close_one_device fs/btrfs/volumes.c:1039 [inline]
RIP: 0010:close_fs_devices.part.44+0x7be/0xa20 fs/btrfs/volumes.c:1063
Code: 48 8d 7b 30 49 89 44 24 18 48 89 f8 48 c1 e8 03 42 80 3c 28 00 0f 85 bd 01 00 00 48 83 6b 30 01 e9 7a fa ff ff e8 82 85 8c fe <0f> 0b e8 7b 85 8c fe 0f 0b e8 74 85 8c fe 0f 0b e9 6f fd ff ff e8
RSP: 0018:ffff8881b7b771d8 EFLAGS: 00010212
RAX: 0000000000040000 RBX: ffff8881cdebb300 RCX: ffffc9000dea2000
RDX: 0000000000022db4 RSI: ffffffff82f3057e RDI: 0000000000000007
RBP: ffff8881b7b77380 R08: ffff8881b50d0000 R09: 0000000000000006
R10: 0000000000000000 R11: ffff8881b50d0000 R12: ffff8881bad2b200
R13: dffffc0000000000 R14: fffffffffffffff4 R15: 0000000000000000
FS:Â 00007fc6d31a2700(0000) GS:ffff8881daf00000(0000) knlGS:0000000000000000
CS:Â 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004dc418 CR3: 00000001d3b95000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with syzbot.