In the Linux kernel, the following vulnerability has been resolved:

mrp: introduce active flags to prevent UAF when applicant uninit

The caller of deltimersync must prevent restarting of the timer, If we have no this synchronization, there is a small probability that the cancellation will not be successful.

And syzbot report the fellowing crash:

BUG: KASAN: use-after-free in hlistaddhead include/linux/list.h:929 [inline] BUG: KASAN: use-after-free in enqueue_timer+0x18/0xa4 kernel/time/timer.c:605 Write at addr f9ff000024df6058 by task syz-fuzzer/2256 Pointer tag: [f9], memory tag: [fe]

CPU: 1 PID: 2256 Comm: syz-fuzzer Not tainted 6.1.0-rc5-syzkaller-00008- ge01d50cbd6ee #0 Hardware name: linux,dummy-virt (DT) Call trace: dumpbacktrace.part.0+0xe0/0xf0 arch/arm64/kernel/stacktrace.c:156 dumpbacktrace arch/arm64/kernel/stacktrace.c:162 [inline] show_stack+0x18/0x40 arch/arm64/kernel/stacktrace.c:163 __dumpstack lib/dumpstack.c:88 [inline] dumpstacklvl+0x68/0x84 lib/dumpstack.c:106 printaddressdescription mm/kasan/report.c:284 [inline] printreport+0x1a8/0x4a0 mm/kasan/report.c:395 kasan_report+0x94/0xb4 mm/kasan/report.c:495 _dokernelfault+0x164/0x1e0 arch/arm64/mm/fault.c:320 dobadarea arch/arm64/mm/fault.c:473 [inline] dotagcheckfault+0x78/0x8c arch/arm64/mm/fault.c:749 domemabort+0x44/0x94 arch/arm64/mm/fault.c:825 el1abort+0x40/0x60 arch/arm64/kernel/entry-common.c:367 el1h64synchandler+0xd8/0xe4 arch/arm64/kernel/entry-common.c:427 el1h64sync+0x64/0x68 arch/arm64/kernel/entry.S:576 hlistaddhead include/linux/list.h:929 [inline] enqueuetimer+0x18/0xa4 kernel/time/timer.c:605 modtimer+0x14/0x20 kernel/time/timer.c:1161 mrpperiodictimerarm net/802/mrp.c:614 [inline] mrpperiodictimer+0xa0/0xc0 net/802/mrp.c:627 calltimerfn.constprop.0+0x24/0x80 kernel/time/timer.c:1474 expiretimers+0x98/0xc4 kernel/time/timer.c:1519

To fix it, we can introduce a new active flags to make sure the timer will not restart.