From 9a8e296958884b807a02759975170b6559901242 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 1 Jun 2026 15:56:38 +0200 Subject: fs: make userspace_init_fs a dynamically-initialized pointer Change userspace_init_fs from a declared-but-unused extern struct to a dynamically initialized pointer. Add init_userspace_fs() which is called early in kernel_init() (PID 1) to record PID 1's fs_struct as the canonical userspace filesystem state. Wire up __override_init_fs() and __revert_init_fs() to actually swap current->fs to/from userspace_init_fs. Previously these were no-ops that stored current->fs back to itself. Fix nullfs_userspace_init() to compare against userspace_init_fs instead of &init_fs. When PID 1 unshares its filesystem state, revert userspace_init_fs to init_fs's root (nullfs) so that stale filesystem state is not silently inherited by kworkers and usermodehelpers. At this stage PID 1's fs still points to rootfs (set by init_mount_tree), so userspace_init_fs points to rootfs and scoped_with_init_fs() is functionally equivalent to its previous no-op behavior. Link: https://patch.msgid.link/20260601-work-kthread-nullfs-v4-5-77ee053060e0@kernel.org Signed-off-by: Christian Brauner (Amutable) --- include/linux/init_task.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index a6cb241ea00c..61536be773f5 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -24,6 +24,7 @@ extern struct files_struct init_files; extern struct fs_struct init_fs; +extern struct fs_struct *userspace_init_fs; extern struct nsproxy init_nsproxy; #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE -- cgit v1.2.3