From 958bd12e79238d69236fcac7ffe1cf2d908cf2e6 Mon Sep 17 00:00:00 2001 From: Thadeu Lima de Souza Cascardo Date: Tue, 9 Aug 2022 14:07:51 -0300 Subject: [PATCH] posix-cpu-timers: Cleanup CPU timers before freeing them during exec Commit d58d6b25301c ("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: d58d6b25301c ("posix-cpu-timers: Store a reference to a pid not a task") Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Thomas Gleixner Reviewed-by: Thomas Gleixner Cc: Link: https://lore.kernel.org/r/20220809170751.164716-1-cascardo@canonical.com --- fs/exec.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index 5fd73915c62ce..f793221f4eb63 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1304,6 +1304,9 @@ 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); flush_itimer_signals(); #endif -- 2.39.5