Commit c1fa0bb633e4 for kernel

commit c1fa0bb633e4a6b11e83ffc57fa5abe8ebb87891
Author: Jann Horn <jannh@google.com>
Date:   Mon May 11 08:55:11 2026 -0700

    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 <jannh@google.com>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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();
 	}