udf: augment UDF permissions on new inodes

Windows presents files created within Linux as read-only, even when
permissions in Linux indicate the file should be writable.

UDF defines a slightly different set of basic file permissions than Linux.
Specifically, UDF has "delete" and "change attribute" permissions for each
access class (user/group/other). Linux has no equivalents for these.

When the Linux UDF driver creates a file (or directory), no UDF delete or
change attribute permissions are granted. The lack of delete permission
appears to cause Windows to mark an item read-only when its permissions
otherwise indicate that it should be read-write.

Fix this by having UDF delete permissions track Linux write permissions.
Also grant UDF change attribute permission to the owner when creating a
new inode.

Reported by: Ty Young
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Link: https://lore.kernel.org/r/20190827121359.9954-1-steve@digidescorp.com
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/file.c

@@ -280,6 +280,9 @@ static int udf_setattr(struct dentry *dentry, struct iattr *attr)
 			return error;
 	}
 
+	if (attr->ia_valid & ATTR_MODE)
+		udf_update_extra_perms(inode, attr->ia_mode);
+
 	setattr_copy(inode, attr);
 	mark_inode_dirty(inode);
 	return 0;