linux-kernel - BUG: spinlock bad magic in lock_timer

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Message-ID: <8d6bd3e.1228f.197cf7e7892.Coremail.baishuoran@hrbeu.edu.cn>
Date: Thu, 3 Jul 2025 16:54:21 +0800 (GMT+08:00)
From: 白烁冉 <baishuoran@...eu.edu.cn>
To: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
	"Frederic Weisbecker" <frederic@...nel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>
Cc: "Kun Hu" <huk23@...udan.edu.cn>, "Jiaji Qin" <jjtan24@...udan.edu.cn>,
	linux-kernel@...r.kernel.org, syzkaller@...glegroups.com
Subject: BUG: spinlock bad magic in lock_timer_base

Dear Maintainers,

When using our customized Syzkaller to fuzz the latest Linux kernel, the following crash (110th)was triggered.

HEAD commit: 6537cfb395f352782918d8ee7b7f10ba2cc3cbf2
git tree: upstream
Output:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/report110.txt 
Kernel config:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/config.txt
C reproducer:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/110repro.c Syzlang 
reproducer:https://github.com/pghk13/Kernel-Bug/blob/main/0702_6.14/BUG%3A%20spinlock%20bad%20magic%20in%20lock_timer_base/110repro.txt Our reproducer uses mounts a constructed filesystem image.

The error occurs in the lock_timer_base (timer.c lines 1770-1790 or so). It happens cleanup_srcu_struct during the KVM VM shutdown process, and it is likely that the memory pointed to by the timer object has been freed. The timer_base pointer returned by the get_timer_base (tf) points to an invalid memory area (__init_begin+0x2a500)
We have reproduced this issue several times on 6.14 again.

If you fix this issue, please add the following tag to the commit:
Reported-by: Kun Hu <huk23@...udan.edu.cn>, Jiaji Qin <jjtan24@...udan.edu.cn>, Shuoran Bai <baishuoran@...eu.edu.cn>

BUG: spinlock bad magic on CPU#2, syz.6.399/18129
 lock: __init_begin+0x2a500/0x41000, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
CPU: 2 UID: 0 PID: 18129 Comm: syz.6.399 Not tainted 6.14.0 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x116/0x1b0
 do_raw_spin_lock+0x22c/0x2e0
 _raw_spin_lock_irqsave+0x45/0x60
 lock_timer_base+0x125/0x1c0
 __try_to_del_timer_sync+0x7f/0x160
 __timer_delete_sync+0x120/0x1c0
 cleanup_srcu_struct+0x122/0x5a0
 kvm_put_kvm+0x7c9/0xa10
 kvm_vcpu_release+0x4b/0x70
 __fput+0x417/0xb60
 __fput_sync+0xa6/0xc0
 __x64_sys_close+0x8b/0x120
 do_syscall_64+0xcf/0x250
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fafdad1ebdb
Code: 03 00 00 00 0f 05 48 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 2f 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007ffde8c95b20 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007fafdad1ebdb
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007ffde8c95bf8 R08: 0000000000000000 R09: 00007fafda8015a6
R10: 0000000000000001 R11: 0000000000000293 R12: 00007fafdafa5fa0
R13: 000000000002f3ea R14: ffffffffffffffff R15: 00007fafdafa5fa0
 </TASK>

thanks,
Kun Hu