vfs: syscall: Add fsopen() to prepare for superblock creation

[linux-block.git] / fs / fsopen.c

diff --git a/fs/fsopen.c b/fs/fsopen.c
new file mode 100644 (file)
index 0000000..d256f1a
--- /dev/null
+++ b/fs/fsopen.c
@@ -0,0 +1,88 @@
+/* Filesystem access-by-fd.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/fs_context.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/syscalls.h>
+#include <linux/security.h>
+#include <linux/anon_inodes.h>
+#include <linux/namei.h>
+#include <linux/file.h>
+#include <uapi/linux/mount.h>
+#include "mount.h"
+
+static int fscontext_release(struct inode *inode, struct file *file)
+{
+       struct fs_context *fc = file->private_data;
+
+       if (fc) {
+               file->private_data = NULL;
+               put_fs_context(fc);
+       }
+       return 0;
+}
+
+const struct file_operations fscontext_fops = {
+       .release        = fscontext_release,
+       .llseek         = no_llseek,
+};
+
+/*
+ * Attach a filesystem context to a file and an fd.
+ */
+static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
+{
+       int fd;
+
+       fd = anon_inode_getfd("fscontext", &fscontext_fops, fc,
+                             O_RDWR | o_flags);
+       if (fd < 0)
+               put_fs_context(fc);
+       return fd;
+}
+
+/*
+ * Open a filesystem by name so that it can be configured for mounting.
+ *
+ * We are allowed to specify a container in which the filesystem will be
+ * opened, thereby indicating which namespaces will be used (notably, which
+ * network namespace will be used for network filesystems).
+ */
+SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
+{
+       struct file_system_type *fs_type;
+       struct fs_context *fc;
+       const char *fs_name;
+
+       if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
+               return -EPERM;
+
+       if (flags & ~FSOPEN_CLOEXEC)
+               return -EINVAL;
+
+       fs_name = strndup_user(_fs_name, PAGE_SIZE);
+       if (IS_ERR(fs_name))
+               return PTR_ERR(fs_name);
+
+       fs_type = get_fs_type(fs_name);
+       kfree(fs_name);
+       if (!fs_type)
+               return -ENODEV;
+
+       fc = fs_context_for_mount(fs_type, 0);
+       put_filesystem(fs_type);
+       if (IS_ERR(fc))
+               return PTR_ERR(fc);
+
+       fc->phase = FS_CONTEXT_CREATE_PARAMS;
+       return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
+}