memfd: make memfd_open() skip fd attributes not needed for vma mapping

There is only one user of memfd_open() outside of memfd.c: open_filemap().
It is restoring a file-backed mapping and doesn't need to F_SETOWN
nor update the fd's position.

Signed-off-by: Michał Mirosław <emmir@google.com>

criu/memfd.c

@@ -355,14 +355,6 @@ int memfd_open(struct file_desc *d, u32 *fdflags)
 	close(fd);
 	fd = _fd;
 
-	if (restore_fown(fd, mfe->fown) < 0)
-		goto err;
-
-	if (lseek(fd, mfe->pos, SEEK_SET) < 0) {
-		pr_perror("Can't restore file position of memfd id=%d", mfe->id);
-		goto err;
-	}
-
 	return fd;
 
 err:
@@ -371,14 +363,26 @@ int memfd_open(struct file_desc *d, u32 *fdflags)
 	return -1;
 }
 
-static int memfd_open_fe_fd(struct file_desc *fd, int *new_fd)
+static int memfd_open_fe_fd(struct file_desc *d, int *new_fd)
 {
-	int tmp;
+	MemfdFileEntry *mfe;
+	int fd;
 
-	tmp = memfd_open(fd, NULL);
-	if (tmp < 0)
+	fd = memfd_open(d, NULL);
+	if (fd < 0)
 		return -1;
-	*new_fd = tmp;
+
+	mfe = container_of(d, struct memfd_info, d)->mfe;
+
+	if (restore_fown(fd, mfe->fown) < 0)
+		goto err;
+
+	if (lseek(fd, mfe->pos, SEEK_SET) < 0) {
+		pr_perror("Can't restore file position of %d for memfd id=%d", fd, mfe->id);
+		goto err;
+	}
+
+	*new_fd = fd;
 	return 0;
 }