WARNING: refcount bug in del_gendisk

[Wei Chen]

Dear Linux Developer,

Recently when using our tool to fuzz kernel, the following crash was triggered:

HEAD commit: 64570fbc14f8 Linux 5.15-rc5
git tree: upstream
compiler: clang 12.0.0
console output:
https://drive.google.com/file/d/1rRIA8DQuvuMXcFn2VKCXJaijxHGIVRRm/view?usp=sharing
kernel config: https://drive.google.com/file/d/1lNwvovjLNrcuyFGrg05IoSmgO5jaKBBJ/view?usp=sharing

Unfortunately, I don't have any reproducer for this crash yet.

refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 26667 at lib/refcount.c:28
refcount_warn_saturate+0x186/0x1d0
Modules linked in:
CPU: 0 PID: 26667 Comm: syz-executor Not tainted 5.15.0-rc5+ #14
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x186/0x1d0
Code: c7 a0 0d 15 8b 31 c0 e8 48 33 21 fd 0f 0b eb 80 e8 4f f9 57 fd
c6 05 23 e7 fb 09 01 48 c7 c7 00 0e 15 8b 31 c0 e8 2a 33 21 fd <0f> 0b
e9 5f ff ff ff e8 2e f9 57 fd c6 05 03 e7 fb 09 01 48 c7 c7
RSP: 0018:ffffc9000c47fd90 EFLAGS: 00010246
RAX: 2c799da371900300 RBX: 0000000000000003 RCX: 0000000000040000
RDX: ffffc90008d39000 RSI: 000000000003ffff RDI: 0000000000040000
RBP: 0000000000000003 R08: ffffffff816a2ede R09: ffffed100c7857a8
R10: ffffed100c7857a8 R11: 0000000000000000 R12: ffff88810504c150
R13: 1ffff11020a09810 R14: ffff888103d93b38 R15: ffff888103d93b00
FS:  00007f74c6c90700(0000) GS:ffff888063c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000556503c79d68 CR3: 00000000460bb000 CR4: 0000000000752ef0
DR0: 0000000020000080 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
PKRU: 55555554
Call Trace:
 kobject_put+0x10d/0x130
 kobject_put+0xce/0x130
 del_gendisk+0x3c9/0x710
 loop_control_ioctl+0x5d7/0x770
 __se_sys_ioctl+0x10a/0x190
 do_syscall_64+0x3d/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f74c9727c4d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f74c6c8fc58 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f74c984e0a0 RCX: 00007f74c9727c4d
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000006
RBP: 00007f74c97a0d80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f74c984e0a0
R13: 00007fffe21bf5cf R14: 00007fffe21bf770 R15: 00007f74c6c8fdc0

Best,
Wei