From a7c11744ca7ca4161f4ad8cdce2986d3ae814e03 Mon Sep 17 00:00:00 2001 From: Thadeu Lima de Souza Cascardo Date: Fri, 22 Jul 2022 06:52:11 -0300 Subject: [PATCH] [PATCH] posix-cpu-timers: Cleanup CPU timers before freeing them during exec Commit 55e8c8eb2c7b ("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: 55e8c8eb2c7b ("posix-cpu-timers: Store a reference to a pid not a task") Reported-by: "An independent security researcher working with SSD Secure Disclosure" Signed-off-by: Thadeu Lima de Souza Cascardo Gbp-Pq: Topic bugfix/all Gbp-Pq: Name posix-cpu-timers-Cleanup-CPU-timers-before-freeing-t.patch --- fs/exec.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index d37a82206fa..b56bc4b4016 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1286,6 +1286,9 @@ 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 -- 2.30.2