Eric W. Biederman 343f4c49f2 kthread: Don't allocate kthread_struct for init and umh ... If kthread_is_per_cpu runs concurrently with free_kthread_struct the kthread_struct that was just freed may be read from. This bug was introduced by commit 40966e316f ("kthread: Ensure struct kthread is present for all kthreads"). When kthread_struct started to be allocated for all tasks that have PF_KTHREAD set. This in turn required the kthread_struct to be freed in kernel_execve and violated the assumption that kthread_struct will have the same lifetime as the task. Looking a bit deeper this only applies to callers of kernel_execve which is just the init process and the user mode helper processes. These processes really don't want to be kernel threads but are for historical reasons. Mostly that copy_thread does not know how to take a kernel mode function to the process with for processes without PF_KTHREAD or PF_IO_WORKER set. Solve this by not allocating kthread_struct for the init process and the user mode helper processes. This is done by adding a kthread member to struct kernel_clone_args. Setting kthread in fork_idle and kernel_thread. Adding user_mode_thread that works like kernel_thread except it does not set kthread. In fork only allocating the kthread_struct if .kthread is set. I have looked at kernel/kthread.c and since commit 40966e316f ("kthread: Ensure struct kthread is present for all kthreads") there have been no assumptions added that to_kthread or __to_kthread will not return NULL. There are a few callers of to_kthread or __to_kthread that assume a non-NULL struct kthread pointer will be returned. These functions are kthread_data(), kthread_parmme(), kthread_exit(), kthread(), kthread_park(), kthread_unpark(), kthread_stop(). All of those functions can reasonably expected to be called when it is know that a task is a kthread so that assumption seems reasonable. Cc: stable@vger.kernel.org Fixes: 40966e316f ("kthread: Ensure struct kthread is present for all kthreads") Reported-by: Максим Кутявин <maximkabox13@gmail.com> Link: https://lkml.kernel.org/r/20220506141512.516114-1-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>		2022-05-06 14:49:44 -05:00
..
calibrate.c	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
do_mounts_initrd.c	Merge branch 'hch.init_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2020-08-07 09:40:34 -07:00
do_mounts_rd.c	init: add an init_unlink helper	2020-07-31 08:17:52 +02:00
do_mounts.c	block: remove genhd.h	2022-02-02 07:49:59 -07:00
do_mounts.h	init: add an init_mknod helper	2020-07-31 08:17:54 +02:00
init_task.c	kcsan: Remove redundant zero-initialization of globals	2021-12-09 16:42:26 -08:00
initramfs.c	memblock: use memblock_free for freeing virtual pointers	2021-11-06 13:30:41 -07:00
Kconfig	Kbuild updates for v5.18	2022-03-31 11:59:03 -07:00
main.c	kthread: Don't allocate kthread_struct for init and umh	2022-05-06 14:49:44 -05:00
Makefile	sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers	2022-03-11 15:36:35 +01:00
noinitramfs.c	init: move usermodehelper_enable() to populate_rootfs()	2021-09-08 11:50:27 -07:00
version.c	kbuild: add an elfnote for whether vmlinux is built with lto	2021-04-25 05:25:42 +09:00