From de77c3a5b95c95a4915142071643d94e3e1ada35 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Fri, 7 Jan 2022 12:18:12 -0600
Subject: [PATCH] exit: Move force_uaccess back into do_exit
Git-commit: de77c3a5b95c95a4915142071643d94e3e1ada35
Patch-mainline: v5.17-rc1
References: bsc#1207328
With kernel threads on architectures that still have set_fs/get_fs
running as KERNEL_DS moving force_uaccess_begin does not appear safe.
Calling force_uaccess_begin is a noop on anything people care about.
Update the comment to explain why this code while looking like an
obvious candidate for moving to make_task_dead probably needs to
remain in do_exit until set_fs/get_fs are entirely removed from the
kernel.
Fixes: 05ea0424f0e2 ("exit: Move oops specific logic from do_exit into make_task_dead")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lkml.kernel.org/r/YdUxGKRcSiDy8jGg@zeniv-ca.linux.org.uk
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
kernel/exit.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index db4eeb7fc680..fc0726cb22db 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -737,6 +737,20 @@ void __noreturn do_exit(long code)
WARN_ON(blk_needs_flush_plug(tsk));
+ /*
+ * If do_dead is called because this processes oopsed, it's possible
+ * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before
+ * continuing. Amongst other possible reasons, this is to prevent
+ * mm_release()->clear_child_tid() from writing to a user-controlled
+ * kernel address.
+ *
+ * On uptodate architectures force_uaccess_begin is a noop. On
+ * architectures that still have set_fs/get_fs in addition to handling
+ * oopses handles kernel threads that run as set_fs(KERNEL_DS) by
+ * default.
+ */
+ force_uaccess_begin();
+
profile_task_exit(tsk);
kcov_task_exit(tsk);
@@ -862,15 +876,6 @@ void __noreturn make_task_dead(int signr)
if (unlikely(!tsk->pid))
panic("Attempted to kill the idle task!");
- /*
- * If make_task_dead is called because this processes oopsed, it's possible
- * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before
- * continuing. Amongst other possible reasons, this is to prevent
- * mm_release()->clear_child_tid() from writing to a user-controlled
- * kernel address.
- */
- force_uaccess_begin();
-
if (unlikely(in_atomic())) {
pr_info("note: %s[%d] exited with preempt_count %d\n",
current->comm, task_pid_nr(current),
--
2.35.3