From original patch by dann frazier <dann.frazier@canonical.com>:
grub_net_fs_open() saves off a copy of the file structure it gets passed and
uses it to create a bufio structure. It then overwrites the passed in file
structure with this new bufio structure. Since file->name doesn't get set
until we return back to grub_file_open(), it means that only the bufio
structure gets a valid file->name. The "real" file's name is left
uninitialized. This leads to a crash when the progress module hook is called
on it.
grub_net_fs_open() already saved copy of file name as ->net->name, so change
progress module to use it.
Also, grub_file_open may leave file->name as NULL if grub_strdup fails. Check
for it.
Also-By: dann frazier <dann.frazier@canonical.com>
Patch-Name: progress_avoid_null_deref.patch
Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1459872
