CVE-2022-50697

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

mrp: introduce active flags to prevent UAF when applicant uninit

The caller of del_timer_sync 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 hlist_add_head 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:

dump_backtrace.part.0+0xe0/0xf0 arch/arm64/kernel/stacktrace.c:156

dump_backtrace arch/arm64/kernel/stacktrace.c:162 [inline]

show_stack+0x18/0x40 arch/arm64/kernel/stacktrace.c:163

__dump_stack lib/dump_stack.c:88 [inline]

dump_stack_lvl+0x68/0x84 lib/dump_stack.c:106

print_address_description mm/kasan/report.c:284 [inline]

print_report+0x1a8/0x4a0 mm/kasan/report.c:395

kasan_report+0x94/0xb4 mm/kasan/report.c:495

__do_kernel_fault+0x164/0x1e0 arch/arm64/mm/fault.c:320

do_bad_area arch/arm64/mm/fault.c:473 [inline]

do_tag_check_fault+0x78/0x8c arch/arm64/mm/fault.c:749

do_mem_abort+0x44/0x94 arch/arm64/mm/fault.c:825

el1_abort+0x40/0x60 arch/arm64/kernel/entry-common.c:367

el1h_64_sync_handler+0xd8/0xe4 arch/arm64/kernel/entry-common.c:427

el1h_64_sync+0x64/0x68 arch/arm64/kernel/entry.S:576

hlist_add_head include/linux/list.h:929 [inline]

enqueue_timer+0x18/0xa4 kernel/time/timer.c:605

mod_timer+0x14/0x20 kernel/time/timer.c:1161

mrp_periodic_timer_arm net/802/mrp.c:614 [inline]

mrp_periodic_timer+0xa0/0xc0 net/802/mrp.c:627

call_timer_fn.constprop.0+0x24/0x80 kernel/time/timer.c:1474

expire_timers+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.