From ef9d66918a7f2e2248e3d5af6146bc573a7e7414 Mon Sep 17 00:00:00 2001 From: Jonathan Maple Date: Tue, 9 Sep 2025 12:25:39 -0400 Subject: [PATCH] posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit jira VULN-136690 jira VULN-136689 cve CVE-2025-38352 commit-author Oleg Nesterov commit f90fff1e152dedf52b932240ebbd670d83330eca upstream-diff There where massive merge conflicts due several commits missing from upstream. Had to manually place and correct do to cherry-pick being extremely greedy with trying to pull changes from this LKML change set: https://lore.kernel.org/all/20200730101404.956367860@linutronix.de/ If an exiting non-autoreaping task has already passed exit_notify() and calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent or debugger right after unlock_task_sighand(). If a concurrent posix_cpu_timer_del() runs at that moment, it won't be able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or lock_task_sighand() will fail. Add the tsk->exit_state check into run_posix_cpu_timers() to fix this. This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because exit_task_work() is called before exit_notify(). But the check still makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail anyway in this case. Cc: stable@vger.kernel.org Reported-by: Benoît Sevens Fixes: 0bdd2ed4138e ("sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()") Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds (cherry picked from commit f90fff1e152dedf52b932240ebbd670d83330eca) Signed-off-by: Jonathan Maple --- kernel/time/posix-cpu-timers.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index d6378f9d0ea5d..bc56c8a602abb 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -1122,6 +1122,15 @@ void run_posix_cpu_timers(void) lockdep_assert_irqs_disabled(); + /* + * Ensure that release_task(tsk) can't happen while + * handle_posix_cpu_timers() is running. Otherwise, a concurrent + * posix_cpu_timer_del() may fail to lock_task_sighand(tsk) and + * miss timer->it.cpu.firing != 0. + */ + if (tsk->exit_state) + return; + /* * The fast path checks that there are no expired thread or thread * group timers. If that's so, just return.