v4.19.13 snapshot.
diff --git a/fs/fhandle.c b/fs/fhandle.c
new file mode 100644
index 0000000..0ee7274
--- /dev/null
+++ b/fs/fhandle.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/syscalls.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/exportfs.h>
+#include <linux/fs_struct.h>
+#include <linux/fsnotify.h>
+#include <linux/personality.h>
+#include <linux/uaccess.h>
+#include <linux/compat.h>
+#include "internal.h"
+#include "mount.h"
+
+static long do_sys_name_to_handle(struct path *path,
+ struct file_handle __user *ufh,
+ int __user *mnt_id)
+{
+ long retval;
+ struct file_handle f_handle;
+ int handle_dwords, handle_bytes;
+ struct file_handle *handle = NULL;
+
+ /*
+ * We need to make sure whether the file system
+ * support decoding of the file handle
+ */
+ if (!path->dentry->d_sb->s_export_op ||
+ !path->dentry->d_sb->s_export_op->fh_to_dentry)
+ return -EOPNOTSUPP;
+
+ if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
+ return -EFAULT;
+
+ if (f_handle.handle_bytes > MAX_HANDLE_SZ)
+ return -EINVAL;
+
+ handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
+ GFP_KERNEL);
+ if (!handle)
+ return -ENOMEM;
+
+ /* convert handle size to multiple of sizeof(u32) */
+ handle_dwords = f_handle.handle_bytes >> 2;
+
+ /* we ask for a non connected handle */
+ retval = exportfs_encode_fh(path->dentry,
+ (struct fid *)handle->f_handle,
+ &handle_dwords, 0);
+ handle->handle_type = retval;
+ /* convert handle size to bytes */
+ handle_bytes = handle_dwords * sizeof(u32);
+ handle->handle_bytes = handle_bytes;
+ if ((handle->handle_bytes > f_handle.handle_bytes) ||
+ (retval == FILEID_INVALID) || (retval == -ENOSPC)) {
+ /* As per old exportfs_encode_fh documentation
+ * we could return ENOSPC to indicate overflow
+ * But file system returned 255 always. So handle
+ * both the values
+ */
+ /*
+ * set the handle size to zero so we copy only
+ * non variable part of the file_handle
+ */
+ handle_bytes = 0;
+ retval = -EOVERFLOW;
+ } else
+ retval = 0;
+ /* copy the mount id */
+ if (put_user(real_mount(path->mnt)->mnt_id, mnt_id) ||
+ copy_to_user(ufh, handle,
+ sizeof(struct file_handle) + handle_bytes))
+ retval = -EFAULT;
+ kfree(handle);
+ return retval;
+}
+
+/**
+ * sys_name_to_handle_at: convert name to handle
+ * @dfd: directory relative to which name is interpreted if not absolute
+ * @name: name that should be converted to handle.
+ * @handle: resulting file handle
+ * @mnt_id: mount id of the file system containing the file
+ * @flag: flag value to indicate whether to follow symlink or not
+ *
+ * @handle->handle_size indicate the space available to store the
+ * variable part of the file handle in bytes. If there is not
+ * enough space, the field is updated to return the minimum
+ * value required.
+ */
+SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
+ struct file_handle __user *, handle, int __user *, mnt_id,
+ int, flag)
+{
+ struct path path;
+ int lookup_flags;
+ int err;
+
+ if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
+ if (flag & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+ err = user_path_at(dfd, name, lookup_flags, &path);
+ if (!err) {
+ err = do_sys_name_to_handle(&path, handle, mnt_id);
+ path_put(&path);
+ }
+ return err;
+}
+
+static struct vfsmount *get_vfsmount_from_fd(int fd)
+{
+ struct vfsmount *mnt;
+
+ if (fd == AT_FDCWD) {
+ struct fs_struct *fs = current->fs;
+ spin_lock(&fs->lock);
+ mnt = mntget(fs->pwd.mnt);
+ spin_unlock(&fs->lock);
+ } else {
+ struct fd f = fdget(fd);
+ if (!f.file)
+ return ERR_PTR(-EBADF);
+ mnt = mntget(f.file->f_path.mnt);
+ fdput(f);
+ }
+ return 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 */
+ *handle = f_handle;
+ if (copy_from_user(&handle->f_handle,
+ &ufh->f_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;
+}
+
+static 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, 0);
+ 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;
+}
+
+#ifdef CONFIG_COMPAT
+/*
+ * Exactly like fs/open.c:sys_open_by_handle_at(), except that it
+ * doesn't set the O_LARGEFILE flag.
+ */
+COMPAT_SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
+ struct file_handle __user *, handle, int, flags)
+{
+ return do_handle_open(mountdirfd, handle, flags);
+}
+#endif