vfs: syscall: Add open_tree(2) to reference or clone a mount
open_tree(dfd, pathname, flags) Returns an O_PATH-opened file descriptor or an error. dfd and pathname specify the location to open, in usual fashion (see e.g. fstatat(2)). flags should be an OR of some of the following: * AT_PATH_EMPTY, AT_NO_AUTOMOUNT, AT_SYMLINK_NOFOLLOW - same meanings as usual * OPEN_TREE_CLOEXEC - make the resulting descriptor close-on-exec * OPEN_TREE_CLONE or OPEN_TREE_CLONE | AT_RECURSIVE - instead of opening the location in question, create a detached mount tree matching the subtree rooted at location specified by dfd/pathname. With AT_RECURSIVE the entire subtree is cloned, without it - only the part within in the mount containing the location in question. In other words, the same as mount --rbind or mount --bind would've taken. The detached tree will be dissolved on the final close of obtained file. Creation of such detached trees requires the same capabilities as doing mount --bind. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-api@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
parent
9e98c678c2
commit
a07b200047
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@ -398,7 +398,8 @@
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384 i386 arch_prctl sys_arch_prctl __ia32_compat_sys_arch_prctl
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385 i386 io_pgetevents sys_io_pgetevents_time32 __ia32_compat_sys_io_pgetevents
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386 i386 rseq sys_rseq __ia32_sys_rseq
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# don't use numbers 387 through 392, add new calls at the end
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387 i386 open_tree sys_open_tree __ia32_sys_open_tree
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# don't use numbers 388 through 392, add new calls at the end
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393 i386 semget sys_semget __ia32_sys_semget
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394 i386 semctl sys_semctl __ia32_compat_sys_semctl
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395 i386 shmget sys_shmget __ia32_sys_shmget
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@ -343,6 +343,7 @@
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332 common statx __x64_sys_statx
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333 common io_pgetevents __x64_sys_io_pgetevents
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334 common rseq __x64_sys_rseq
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335 common open_tree __x64_sys_open_tree
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# don't use numbers 387 through 423, add new calls after the last
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# 'common' entry
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424 common pidfd_send_signal __x64_sys_pidfd_send_signal
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@ -255,6 +255,7 @@ static void __fput(struct file *file)
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struct dentry *dentry = file->f_path.dentry;
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struct vfsmount *mnt = file->f_path.mnt;
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struct inode *inode = file->f_inode;
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fmode_t mode = file->f_mode;
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if (unlikely(!(file->f_mode & FMODE_OPENED)))
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goto out;
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@ -277,18 +278,20 @@ static void __fput(struct file *file)
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if (file->f_op->release)
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file->f_op->release(inode, file);
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if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
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!(file->f_mode & FMODE_PATH))) {
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!(mode & FMODE_PATH))) {
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cdev_put(inode->i_cdev);
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}
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fops_put(file->f_op);
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put_pid(file->f_owner.pid);
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if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
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if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
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i_readcount_dec(inode);
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if (file->f_mode & FMODE_WRITER) {
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if (mode & FMODE_WRITER) {
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put_write_access(inode);
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__mnt_drop_write(mnt);
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}
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dput(dentry);
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if (unlikely(mode & FMODE_NEED_UNMOUNT))
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dissolve_on_fput(mnt);
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mntput(mnt);
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out:
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file_free(file);
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@ -94,6 +94,7 @@ extern int __mnt_want_write_file(struct file *);
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extern void __mnt_drop_write(struct vfsmount *);
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extern void __mnt_drop_write_file(struct file *);
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extern void dissolve_on_fput(struct vfsmount *);
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/*
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* fs_struct.c
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*/
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157
fs/namespace.c
157
fs/namespace.c
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@ -20,6 +20,7 @@
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#include <linux/init.h> /* init_rootfs */
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#include <linux/fs_struct.h> /* get_fs_root et.al. */
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#include <linux/fsnotify.h> /* fsnotify_vfsmount_delete */
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#include <linux/file.h>
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#include <linux/uaccess.h>
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#include <linux/proc_ns.h>
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#include <linux/magic.h>
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@ -1832,6 +1833,21 @@ struct vfsmount *collect_mounts(const struct path *path)
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return &tree->mnt;
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}
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static void free_mnt_ns(struct mnt_namespace *);
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static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
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void dissolve_on_fput(struct vfsmount *mnt)
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{
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struct mnt_namespace *ns;
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namespace_lock();
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lock_mount_hash();
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ns = real_mount(mnt)->mnt_ns;
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umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
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unlock_mount_hash();
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namespace_unlock();
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free_mnt_ns(ns);
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}
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void drop_collected_mounts(struct vfsmount *mnt)
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{
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namespace_lock();
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@ -2222,6 +2238,30 @@ static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
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return false;
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}
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static struct mount *__do_loopback(struct path *old_path, int recurse)
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{
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struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
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if (IS_MNT_UNBINDABLE(old))
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return mnt;
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if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
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return mnt;
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if (!recurse && has_locked_children(old, old_path->dentry))
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return mnt;
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if (recurse)
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mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE);
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else
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mnt = clone_mnt(old, old_path->dentry, 0);
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if (!IS_ERR(mnt))
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mnt->mnt.mnt_flags &= ~MNT_LOCKED;
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return mnt;
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}
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/*
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* do loopback mount.
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*/
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@ -2229,7 +2269,7 @@ static int do_loopback(struct path *path, const char *old_name,
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int recurse)
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{
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struct path old_path;
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struct mount *mnt = NULL, *old, *parent;
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struct mount *mnt = NULL, *parent;
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struct mountpoint *mp;
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int err;
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if (!old_name || !*old_name)
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@ -2243,38 +2283,21 @@ static int do_loopback(struct path *path, const char *old_name,
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goto out;
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mp = lock_mount(path);
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err = PTR_ERR(mp);
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if (IS_ERR(mp))
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if (IS_ERR(mp)) {
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err = PTR_ERR(mp);
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goto out;
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}
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old = real_mount(old_path.mnt);
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parent = real_mount(path->mnt);
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err = -EINVAL;
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if (IS_MNT_UNBINDABLE(old))
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goto out2;
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if (!check_mnt(parent))
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goto out2;
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if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations)
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goto out2;
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if (!recurse && has_locked_children(old, old_path.dentry))
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goto out2;
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if (recurse)
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mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE);
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else
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mnt = clone_mnt(old, old_path.dentry, 0);
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mnt = __do_loopback(&old_path, recurse);
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if (IS_ERR(mnt)) {
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err = PTR_ERR(mnt);
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goto out2;
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}
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mnt->mnt.mnt_flags &= ~MNT_LOCKED;
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err = graft_tree(mnt, parent, mp);
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if (err) {
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lock_mount_hash();
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@ -2288,6 +2311,96 @@ out:
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return err;
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}
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static struct file *open_detached_copy(struct path *path, bool recursive)
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{
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struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
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struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
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struct mount *mnt, *p;
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struct file *file;
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if (IS_ERR(ns))
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return ERR_CAST(ns);
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namespace_lock();
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mnt = __do_loopback(path, recursive);
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if (IS_ERR(mnt)) {
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namespace_unlock();
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free_mnt_ns(ns);
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return ERR_CAST(mnt);
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}
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lock_mount_hash();
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for (p = mnt; p; p = next_mnt(p, mnt)) {
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p->mnt_ns = ns;
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ns->mounts++;
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}
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ns->root = mnt;
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list_add_tail(&ns->list, &mnt->mnt_list);
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mntget(&mnt->mnt);
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unlock_mount_hash();
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namespace_unlock();
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mntput(path->mnt);
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path->mnt = &mnt->mnt;
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file = dentry_open(path, O_PATH, current_cred());
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if (IS_ERR(file))
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dissolve_on_fput(path->mnt);
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else
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file->f_mode |= FMODE_NEED_UNMOUNT;
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return file;
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}
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SYSCALL_DEFINE3(open_tree, int, dfd, const char *, filename, unsigned, flags)
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{
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struct file *file;
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struct path path;
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int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
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bool detached = flags & OPEN_TREE_CLONE;
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int error;
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int fd;
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BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);
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if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE |
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AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE |
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OPEN_TREE_CLOEXEC))
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return -EINVAL;
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if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE)
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return -EINVAL;
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if (flags & AT_NO_AUTOMOUNT)
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lookup_flags &= ~LOOKUP_AUTOMOUNT;
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if (flags & AT_SYMLINK_NOFOLLOW)
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lookup_flags &= ~LOOKUP_FOLLOW;
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if (flags & AT_EMPTY_PATH)
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lookup_flags |= LOOKUP_EMPTY;
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if (detached && !may_mount())
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return -EPERM;
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fd = get_unused_fd_flags(flags & O_CLOEXEC);
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if (fd < 0)
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return fd;
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error = user_path_at(dfd, filename, lookup_flags, &path);
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if (unlikely(error)) {
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file = ERR_PTR(error);
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} else {
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if (detached)
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file = open_detached_copy(&path, flags & AT_RECURSIVE);
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else
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file = dentry_open(&path, O_PATH, current_cred());
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path_put(&path);
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}
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if (IS_ERR(file)) {
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put_unused_fd(fd);
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return PTR_ERR(file);
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}
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fd_install(fd, file);
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return fd;
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}
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/*
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* Don't allow locked mount flags to be cleared.
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*
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@ -162,10 +162,13 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
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#define FMODE_NONOTIFY ((__force fmode_t)0x4000000)
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/* File is capable of returning -EAGAIN if I/O will block */
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#define FMODE_NOWAIT ((__force fmode_t)0x8000000)
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#define FMODE_NOWAIT ((__force fmode_t)0x8000000)
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/* File represents mount that needs unmounting */
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#define FMODE_NEED_UNMOUNT ((__force fmode_t)0x10000000)
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/* File does not contribute to nr_files count */
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#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000)
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#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000)
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/*
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* Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
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@ -985,6 +985,7 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
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unsigned mask, struct statx __user *buffer);
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asmlinkage long sys_rseq(struct rseq __user *rseq, uint32_t rseq_len,
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int flags, uint32_t sig);
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asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags);
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asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
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siginfo_t __user *info,
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unsigned int flags);
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@ -91,5 +91,7 @@
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#define AT_STATX_FORCE_SYNC 0x2000 /* - Force the attributes to be sync'd with the server */
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#define AT_STATX_DONT_SYNC 0x4000 /* - Don't sync attributes with the server */
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#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
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#endif /* _UAPI_LINUX_FCNTL_H */
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#define MS_MGC_VAL 0xC0ED0000
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#define MS_MGC_MSK 0xffff0000
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/*
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* open_tree() flags.
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*/
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#define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */
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#define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */
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#endif /* _UAPI_LINUX_MOUNT_H */
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