[syzbot] [wireguard?] KCSAN: data-race in wg_expired_retransmit_handshake / wg_packet_send_queued_handshake_initiation (4)

Hello,

syzbot found the following issue on:

HEAD commit:    5ee8dbf54602 Merge tag 'fsverity-for-linus' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=123477e6580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6b32b22d8934c136
dashboard link: https://syzkaller.appspot.com/bug?extid=4ca9a7b9d61b76d0177c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/dacfe44e33b2/disk-5ee8dbf5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/10e825a65a06/vmlinux-5ee8dbf5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b2fe6914587d/bzImage-5ee8dbf5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

==================================================================
BUG: KCSAN: data-race in wg_expired_retransmit_handshake / wg_packet_send_queued_handshake_initiation

read to 0xffff88810b667808 of 4 bytes by interrupt on cpu 0:
 wg_expired_retransmit_handshake+0x2a/0x160 drivers/net/wireguard/timers.c:46
 call_timer_fn+0x3b/0x2a0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2373 [inline]
 __run_timer_base+0x426/0x620 kernel/time/timer.c:2385
 run_timer_base kernel/time/timer.c:2394 [inline]
 run_timer_softirq+0x31/0x70 kernel/time/timer.c:2404
 handle_softirqs+0xb9/0x2a0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x39/0xc0 kernel/softirq.c:723
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0x74/0x80 arch/x86/kernel/apic/apic.c:1056
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
 native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
 pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
 arch_safe_halt arch/x86/kernel/process.c:766 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x3b/0x60 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:191 [inline]
 do_idle+0xcd/0x230 kernel/sched/idle.c:332
 cpu_startup_entry+0x24/0x30 kernel/sched/idle.c:430
 rest_init+0xee/0xf0 init/main.c:760
 start_kernel+0x49a/0x4c0 init/main.c:1210
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0xfc/0x100 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x147

write to 0xffff88810b667808 of 4 bytes by interrupt on cpu 1:
 wg_packet_send_queued_handshake_initiation+0x32/0x180 drivers/net/wireguard/send.c:59
 wg_expired_new_handshake+0x26/0x30 drivers/net/wireguard/timers.c:104
 call_timer_fn+0x3b/0x2a0 kernel/time/timer.c:1748
 expire_timers kernel/time/timer.c:1799 [inline]
 __run_timers kernel/time/timer.c:2373 [inline]
 __run_timer_base+0x426/0x620 kernel/time/timer.c:2385
 run_timer_base kernel/time/timer.c:2394 [inline]
 run_timer_softirq+0x31/0x70 kernel/time/timer.c:2404
 handle_softirqs+0xb9/0x2a0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x39/0xc0 kernel/softirq.c:723
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0x74/0x80 arch/x86/kernel/apic/apic.c:1056
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
 native_safe_halt arch/x86/include/asm/irqflags.h:48 [inline]
 pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:62
 arch_safe_halt arch/x86/kernel/process.c:766 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x3b/0x60 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:191 [inline]
 do_idle+0xcd/0x230 kernel/sched/idle.c:332
 cpu_startup_entry+0x24/0x30 kernel/sched/idle.c:430
 start_secondary+0x95/0xa0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x147

value changed: 0x00000002 -> 0x00000003

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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