fs: prevent out-of-bounds array speculation when closing a file descriptor

commit 609d544414 upstream.

Google-Bug-Id: 114199369
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/file.c

@@ -646,6 +646,7 @@ static struct file *pick_file(struct files_struct *files, unsigned fd)
 		file = ERR_PTR(-EINVAL);
 		goto out_unlock;
 	}
+	fd = array_index_nospec(fd, fdt->max_fds);
 	file = fdt->fd[fd];
 	if (!file) {
 		file = ERR_PTR(-EBADF);