posix-cpu-timers: Cleanup CPU timers before freeing them during exec

mainline inclusion
from mainline-v6.0-rc1
commit e362359a
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5LJH2
CVE: CVE-2022-2585

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e362359ace6f87c201531872486ff295df306d13

--------------------------------

Commit 55e8c8eb ("posix-cpu-timers: Store a reference to a pid not a
task") started looking up tasks by PID when deleting a CPU timer.

When a non-leader thread calls execve, it will switch PIDs with the leader
process. Then, as it calls exit_itimers, posix_cpu_timer_del cannot find
the task because the timer still points out to the old PID.

That means that armed timers won't be disarmed, that is, they won't be
removed from the timerqueue_list. exit_itimers will still release their
memory, and when that list is later processed, it leads to a
use-after-free.

Clean up the timers from the de-threaded task before freeing them. This
prevents a reported use-after-free.

Fixes: 55e8c8eb ("posix-cpu-timers: Store a reference to a pid not a task")
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220809170751.164716-1-cascardo@canonical.com

Conflicts:
	fs/exec.c
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

fs/exec.c

@@ -1274,6 +1274,9 @@ int begin_new_exec(struct linux_binprm * bprm)
 	bprm->mm = NULL;
 
 #ifdef CONFIG_POSIX_TIMERS
+	spin_lock_irq(&me->sighand->siglock);
+	posix_cpu_timers_exit(me);
+	spin_unlock_irq(&me->sighand->siglock);
 	exit_itimers(me->signal);
 	flush_itimer_signals();
 #endif