vfs: Add open by file handle support

[AV: duplicate of open() guts removed; file_open_root() used instead]

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 158 insertions, 0 deletions

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 9f79e743a84..bf93ad2bee0 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -5,6 +5,8 @@
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/exportfs.h>
+#include <linux/fs_struct.h>
+#include <linux/fsnotify.h>
 #include <asm/uaccess.h>
 #include "internal.h"
 
@@ -105,3 +107,159 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
         }
         return err;
 }
+
+static struct vfsmount *get_vfsmount_from_fd(int fd)
+{
+        struct path path;
+
+        if (fd == AT_FDCWD) {
+                struct fs_struct *fs = current->fs;
+                spin_lock(&fs->lock);
+                path = fs->pwd;
+                mntget(path.mnt);
+                spin_unlock(&fs->lock);
+        } else {
+                int fput_needed;
+                struct file *file = fget_light(fd, &fput_needed);
+                if (!file)
+                        return ERR_PTR(-EBADF);
+                path = file->f_path;
+                mntget(path.mnt);
+                fput_light(file, fput_needed);
+        }
+        return path.mnt;
+}
+
+static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
+{
+        return 1;
+}
+
+static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
+                             struct path *path)
+{
+        int retval = 0;
+        int handle_dwords;
+
+        path->mnt = get_vfsmount_from_fd(mountdirfd);
+        if (IS_ERR(path->mnt)) {
+                retval = PTR_ERR(path->mnt);
+                goto out_err;
+        }
+        /* change the handle size to multiple of sizeof(u32) */
+        handle_dwords = handle->handle_bytes >> 2;
+        path->dentry = exportfs_decode_fh(path->mnt,
+                                          (struct fid *)handle->f_handle,
+                                          handle_dwords, handle->handle_type,
+                                          vfs_dentry_acceptable, NULL);
+        if (IS_ERR(path->dentry)) {
+                retval = PTR_ERR(path->dentry);
+                goto out_mnt;
+        }
+        return 0;
+out_mnt:
+        mntput(path->mnt);
+out_err:
+        return retval;
+}
+
+static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
+                   struct path *path)
+{
+        int retval = 0;
+        struct file_handle f_handle;
+        struct file_handle *handle = NULL;
+
+        /*
+         * With handle we don't look at the execute bit on the
+         * the directory. Ideally we would like CAP_DAC_SEARCH.
+         * But we don't have that
+         */
+        if (!capable(CAP_DAC_READ_SEARCH)) {
+                retval = -EPERM;
+                goto out_err;
+        }
+        if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
+                retval = -EFAULT;
+                goto out_err;
+        }
+        if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
+            (f_handle.handle_bytes == 0)) {
+                retval = -EINVAL;
+                goto out_err;
+        }
+        handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+                         GFP_KERNEL);
+        if (!handle) {
+                retval = -ENOMEM;
+                goto out_err;
+        }
+        /* copy the full handle */
+        if (copy_from_user(handle, ufh,
+                           sizeof(struct file_handle) +
+                           f_handle.handle_bytes)) {
+                retval = -EFAULT;
+                goto out_handle;
+        }
+
+        retval = do_handle_to_path(mountdirfd, handle, path);
+
+out_handle:
+        kfree(handle);
+out_err:
+        return retval;
+}
+
+long do_handle_open(int mountdirfd,
+                    struct file_handle __user *ufh, int open_flag)
+{
+        long retval = 0;
+        struct path path;
+        struct file *file;
+        int fd;
+
+        retval = handle_to_path(mountdirfd, ufh, &path);
+        if (retval)
+                return retval;
+
+        fd = get_unused_fd_flags(open_flag);
+        if (fd < 0) {
+                path_put(&path);
+                return fd;
+        }
+        file = file_open_root(path.dentry, path.mnt, "", open_flag);
+        if (IS_ERR(file)) {
+                put_unused_fd(fd);
+                retval =  PTR_ERR(file);
+        } else {
+                retval = fd;
+                fsnotify_open(file);
+                fd_install(fd, file);
+        }
+        path_put(&path);
+        return retval;
+}
+
+/**
+ * sys_open_by_handle_at: Open the file handle
+ * @mountdirfd: directory file descriptor
+ * @handle: file handle to be opened
+ * @flag: open flags.
+ *
+ * @mountdirfd indicate the directory file descriptor
+ * of the mount point. file handle is decoded relative
+ * to the vfsmount pointed by the @mountdirfd. @flags
+ * value is same as the open(2) flags.
+ */
+SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
+                struct file_handle __user *, handle,
+                int, flags)
+{
+        long ret;
+
+        if (force_o_largefile())
+                flags |= O_LARGEFILE;
+
+        ret = do_handle_open(mountdirfd, handle, flags);
+        return ret;
+}