From c1fa0bb633e4a6b11e83ffc57fa5abe8ebb87891 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Mon, 11 May 2026 08:55:11 -0700 Subject: [PATCH] exit: prevent preemption of oopsing TASK_DEAD task When an already-exiting task oopses, make_task_dead() currently calls do_task_dead() with preemption enabled. That is forbidden: do_task_dead() calls __schedule(), which has a comment saying "WARNING: must be called with preemption disabled!". If an oopsing task is preempted in do_task_dead(), between becoming TASK_DEAD and entering the scheduler explicitly, bad things happen: finish_task_switch() assumes that once the scheduler has switched away from a TASK_DEAD task, the task can never run again and its stack is no longer needed; but that assumption apparently doesn't hold if the dead task was preempted (the SM_PREEMPT case). This means that the scheduler ends up repeatedly dropping references on the dead task's stack, which can lead to use-after-free or double-free of the entire task stack; in other words, two tasks can end up running on the same stack, resulting in various kinds of memory corruption. (This does not just affect "recursively oopsing" tasks; it is enough to oops once during task exit, for example in a file_operations::release handler) Fixes: 7f80a2fd7db9 ("exit: Stop poorly open coding do_task_dead in make_task_dead") Cc: stable@kernel.org Signed-off-by: Jann Horn Acked-by: Peter Zijlstra Signed-off-by: Linus Torvalds --- kernel/exit.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/exit.c b/kernel/exit.c index 25e9cb6de7e7..9a909993ab1d 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -1073,6 +1073,7 @@ void __noreturn make_task_dead(int signr) futex_exit_recursive(tsk); tsk->exit_state = EXIT_DEAD; refcount_inc(&tsk->rcu_users); + preempt_disable(); do_task_dead(); }