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authorDavid Howells <dhowells@redhat.com>2018-11-01 23:36:14 +0000
committerAl Viro <viro@zeniv.linux.org.uk>2019-03-20 18:49:06 -0400
commit93766fbd2696c2c4453dd8e1070977e9cd4e6b6d (patch)
treea69eb54819cec4a45ce2ce7953c71faea6a6e79f /fs/namespace.c
parentecdab150fddb42fe6a739335257949220033b782 (diff)
vfs: syscall: Add fsmount() to create a mount for a superblock
Provide a system call by which a filesystem opened with fsopen() and configured by a series of fsconfig() calls can have a detached mount object created for it. This mount object can then be attached to the VFS mount hierarchy using move_mount() by passing the returned file descriptor as the from directory fd. The system call looks like: int mfd = fsmount(int fsfd, unsigned int flags, unsigned int attr_flags); where fsfd is the file descriptor returned by fsopen(). flags can be 0 or FSMOUNT_CLOEXEC. attr_flags is a bitwise-OR of the following flags: MOUNT_ATTR_RDONLY Mount read-only MOUNT_ATTR_NOSUID Ignore suid and sgid bits MOUNT_ATTR_NODEV Disallow access to device special files MOUNT_ATTR_NOEXEC Disallow program execution MOUNT_ATTR__ATIME Setting on how atime should be updated MOUNT_ATTR_RELATIME - Update atime relative to mtime/ctime MOUNT_ATTR_NOATIME - Do not update access times MOUNT_ATTR_STRICTATIME - Always perform atime updates MOUNT_ATTR_NODIRATIME Do not update directory access times In the event that fsmount() fails, it may be possible to get an error message by calling read() on fsfd. If no message is available, ENODATA will be reported. Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-api@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c146
1 files changed, 143 insertions, 3 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 1e72d19fa4f8..3357c3d65475 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3334,9 +3334,149 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
}
/*
- * Move a mount from one place to another.
- * In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be
- * used to copy a mount subtree.
+ * Create a kernel mount representation for a new, prepared superblock
+ * (specified by fs_fd) and attach to an open_tree-like file descriptor.
+ */
+SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
+ unsigned int, attr_flags)
+{
+ struct mnt_namespace *ns;
+ struct fs_context *fc;
+ struct file *file;
+ struct path newmount;
+ struct mount *mnt;
+ struct fd f;
+ unsigned int mnt_flags = 0;
+ long ret;
+
+ if (!may_mount())
+ return -EPERM;
+
+ if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
+ return -EINVAL;
+
+ if (attr_flags & ~(MOUNT_ATTR_RDONLY |
+ MOUNT_ATTR_NOSUID |
+ MOUNT_ATTR_NODEV |
+ MOUNT_ATTR_NOEXEC |
+ MOUNT_ATTR__ATIME |
+ MOUNT_ATTR_NODIRATIME))
+ return -EINVAL;
+
+ if (attr_flags & MOUNT_ATTR_RDONLY)
+ mnt_flags |= MNT_READONLY;
+ if (attr_flags & MOUNT_ATTR_NOSUID)
+ mnt_flags |= MNT_NOSUID;
+ if (attr_flags & MOUNT_ATTR_NODEV)
+ mnt_flags |= MNT_NODEV;
+ if (attr_flags & MOUNT_ATTR_NOEXEC)
+ mnt_flags |= MNT_NOEXEC;
+ if (attr_flags & MOUNT_ATTR_NODIRATIME)
+ mnt_flags |= MNT_NODIRATIME;
+
+ switch (attr_flags & MOUNT_ATTR__ATIME) {
+ case MOUNT_ATTR_STRICTATIME:
+ break;
+ case MOUNT_ATTR_NOATIME:
+ mnt_flags |= MNT_NOATIME;
+ break;
+ case MOUNT_ATTR_RELATIME:
+ mnt_flags |= MNT_RELATIME;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ f = fdget(fs_fd);
+ if (!f.file)
+ return -EBADF;
+
+ ret = -EINVAL;
+ if (f.file->f_op != &fscontext_fops)
+ goto err_fsfd;
+
+ fc = f.file->private_data;
+
+ ret = mutex_lock_interruptible(&fc->uapi_mutex);
+ if (ret < 0)
+ goto err_fsfd;
+
+ /* There must be a valid superblock or we can't mount it */
+ ret = -EINVAL;
+ if (!fc->root)
+ goto err_unlock;
+
+ ret = -EPERM;
+ if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
+ pr_warn("VFS: Mount too revealing\n");
+ goto err_unlock;
+ }
+
+ ret = -EBUSY;
+ if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
+ goto err_unlock;
+
+ ret = -EPERM;
+ if ((fc->sb_flags & SB_MANDLOCK) && !may_mandlock())
+ goto err_unlock;
+
+ newmount.mnt = vfs_create_mount(fc);
+ if (IS_ERR(newmount.mnt)) {
+ ret = PTR_ERR(newmount.mnt);
+ goto err_unlock;
+ }
+ newmount.dentry = dget(fc->root);
+ newmount.mnt->mnt_flags = mnt_flags;
+
+ /* We've done the mount bit - now move the file context into more or
+ * less the same state as if we'd done an fspick(). We don't want to
+ * do any memory allocation or anything like that at this point as we
+ * don't want to have to handle any errors incurred.
+ */
+ vfs_clean_context(fc);
+
+ ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
+ if (IS_ERR(ns)) {
+ ret = PTR_ERR(ns);
+ goto err_path;
+ }
+ mnt = real_mount(newmount.mnt);
+ mnt->mnt_ns = ns;
+ ns->root = mnt;
+ ns->mounts = 1;
+ list_add(&mnt->mnt_list, &ns->list);
+
+ /* Attach to an apparent O_PATH fd with a note that we need to unmount
+ * it, not just simply put it.
+ */
+ file = dentry_open(&newmount, O_PATH, fc->cred);
+ if (IS_ERR(file)) {
+ dissolve_on_fput(newmount.mnt);
+ ret = PTR_ERR(file);
+ goto err_path;
+ }
+ file->f_mode |= FMODE_NEED_UNMOUNT;
+
+ ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
+ if (ret >= 0)
+ fd_install(ret, file);
+ else
+ fput(file);
+
+err_path:
+ path_put(&newmount);
+err_unlock:
+ mutex_unlock(&fc->uapi_mutex);
+err_fsfd:
+ fdput(f);
+ return ret;
+}
+
+/*
+ * Move a mount from one place to another. In combination with
+ * fsopen()/fsmount() this is used to install a new mount and in combination
+ * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
+ * a mount subtree.
*
* Note the flags value is a combination of MOVE_MOUNT_* flags.
*/