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fs: add init_pivot_root()
We will soon be able to pivot_root() with the introduction of the immutable rootfs. Add a wrapper for kernel internal usage. Link: https://patch.msgid.link/20260112-work-immutable-rootfs-v2-2-88dd1c34a204@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner
parent
a2062463e8
commit
3c1b73fc6a
4 changed files with 91 additions and 65 deletions
17
fs/init.c
17
fs/init.c
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@ -13,6 +13,23 @@
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#include <linux/security.h>
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#include "internal.h"
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int __init init_pivot_root(const char *new_root, const char *put_old)
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{
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struct path new_path __free(path_put) = {};
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struct path old_path __free(path_put) = {};
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int ret;
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ret = kern_path(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new_path);
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if (ret)
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return ret;
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ret = kern_path(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_path);
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if (ret)
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return ret;
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return path_pivot_root(&new_path, &old_path);
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}
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int __init init_mount(const char *dev_name, const char *dir_name,
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const char *type_page, unsigned long flags, void *data_page)
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{
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@ -90,6 +90,7 @@ extern bool may_mount(void);
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int path_mount(const char *dev_name, const struct path *path,
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const char *type_page, unsigned long flags, void *data_page);
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int path_umount(const struct path *path, int flags);
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int path_pivot_root(struct path *new, struct path *old);
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int show_path(struct seq_file *m, struct dentry *root);
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137
fs/namespace.c
137
fs/namespace.c
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@ -4498,6 +4498,77 @@ bool path_is_under(const struct path *path1, const struct path *path2)
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}
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EXPORT_SYMBOL(path_is_under);
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int path_pivot_root(struct path *new, struct path *old)
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{
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struct path root __free(path_put) = {};
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struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
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int error;
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if (!may_mount())
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return -EPERM;
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error = security_sb_pivotroot(old, new);
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if (error)
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return error;
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get_fs_root(current->fs, &root);
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LOCK_MOUNT(old_mp, old);
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old_mnt = old_mp.parent;
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if (IS_ERR(old_mnt))
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return PTR_ERR(old_mnt);
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new_mnt = real_mount(new->mnt);
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root_mnt = real_mount(root.mnt);
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ex_parent = new_mnt->mnt_parent;
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root_parent = root_mnt->mnt_parent;
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if (IS_MNT_SHARED(old_mnt) ||
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IS_MNT_SHARED(ex_parent) ||
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IS_MNT_SHARED(root_parent))
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return -EINVAL;
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if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
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return -EINVAL;
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if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
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return -EINVAL;
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if (d_unlinked(new->dentry))
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return -ENOENT;
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if (new_mnt == root_mnt || old_mnt == root_mnt)
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return -EBUSY; /* loop, on the same file system */
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if (!path_mounted(&root))
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return -EINVAL; /* not a mountpoint */
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if (!mnt_has_parent(root_mnt))
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return -EINVAL; /* absolute root */
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if (!path_mounted(new))
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return -EINVAL; /* not a mountpoint */
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if (!mnt_has_parent(new_mnt))
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return -EINVAL; /* absolute root */
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/* make sure we can reach put_old from new_root */
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if (!is_path_reachable(old_mnt, old_mp.mp->m_dentry, new))
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return -EINVAL;
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/* make certain new is below the root */
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if (!is_path_reachable(new_mnt, new->dentry, &root))
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return -EINVAL;
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lock_mount_hash();
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umount_mnt(new_mnt);
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if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
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new_mnt->mnt.mnt_flags |= MNT_LOCKED;
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root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
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}
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/* mount new_root on / */
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attach_mnt(new_mnt, root_parent, root_mnt->mnt_mp);
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umount_mnt(root_mnt);
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/* mount old root on put_old */
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attach_mnt(root_mnt, old_mnt, old_mp.mp);
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touch_mnt_namespace(current->nsproxy->mnt_ns);
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/* A moved mount should not expire automatically */
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list_del_init(&new_mnt->mnt_expire);
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unlock_mount_hash();
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mnt_notify_add(root_mnt);
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mnt_notify_add(new_mnt);
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chroot_fs_refs(&root, new);
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return 0;
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}
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/*
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* pivot_root Semantics:
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* Moves the root file system of the current process to the directory put_old,
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@ -4528,13 +4599,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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{
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struct path new __free(path_put) = {};
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struct path old __free(path_put) = {};
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struct path root __free(path_put) = {};
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struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
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int error;
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if (!may_mount())
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return -EPERM;
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error = user_path_at(AT_FDCWD, new_root,
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LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new);
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if (error)
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@ -4545,66 +4611,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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if (error)
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return error;
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error = security_sb_pivotroot(&old, &new);
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if (error)
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return error;
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get_fs_root(current->fs, &root);
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LOCK_MOUNT(old_mp, &old);
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old_mnt = old_mp.parent;
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if (IS_ERR(old_mnt))
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return PTR_ERR(old_mnt);
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new_mnt = real_mount(new.mnt);
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root_mnt = real_mount(root.mnt);
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ex_parent = new_mnt->mnt_parent;
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root_parent = root_mnt->mnt_parent;
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if (IS_MNT_SHARED(old_mnt) ||
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IS_MNT_SHARED(ex_parent) ||
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IS_MNT_SHARED(root_parent))
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return -EINVAL;
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if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
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return -EINVAL;
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if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
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return -EINVAL;
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if (d_unlinked(new.dentry))
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return -ENOENT;
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if (new_mnt == root_mnt || old_mnt == root_mnt)
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return -EBUSY; /* loop, on the same file system */
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if (!path_mounted(&root))
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return -EINVAL; /* not a mountpoint */
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if (!mnt_has_parent(root_mnt))
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return -EINVAL; /* absolute root */
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if (!path_mounted(&new))
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return -EINVAL; /* not a mountpoint */
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if (!mnt_has_parent(new_mnt))
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return -EINVAL; /* absolute root */
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/* make sure we can reach put_old from new_root */
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if (!is_path_reachable(old_mnt, old_mp.mp->m_dentry, &new))
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return -EINVAL;
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/* make certain new is below the root */
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if (!is_path_reachable(new_mnt, new.dentry, &root))
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return -EINVAL;
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lock_mount_hash();
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umount_mnt(new_mnt);
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if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
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new_mnt->mnt.mnt_flags |= MNT_LOCKED;
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root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
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}
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/* mount new_root on / */
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attach_mnt(new_mnt, root_parent, root_mnt->mnt_mp);
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umount_mnt(root_mnt);
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/* mount old root on put_old */
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attach_mnt(root_mnt, old_mnt, old_mp.mp);
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touch_mnt_namespace(current->nsproxy->mnt_ns);
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/* A moved mount should not expire automatically */
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list_del_init(&new_mnt->mnt_expire);
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unlock_mount_hash();
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mnt_notify_add(root_mnt);
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mnt_notify_add(new_mnt);
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chroot_fs_refs(&root, &new);
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return 0;
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return path_pivot_root(&new, &old);
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}
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static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt)
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@ -17,3 +17,4 @@ int __init init_mkdir(const char *pathname, umode_t mode);
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int __init init_rmdir(const char *pathname);
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int __init init_utimes(char *filename, struct timespec64 *ts);
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int __init init_dup(struct file *file);
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int __init init_pivot_root(const char *new_root, const char *put_old);
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