[Info-mtools] Bug: File or directory is lost after renaming it to "Õtest"

[Pali Rohár]

Hi! More mtools programs (mlabel, mcopy, mdir) do not handle correctly
file names which starts with 0x05 or 0xE5 byte.

In FAT specification is written:

 * If DIR_Name[0] == 0xE5, then the directory entry is free (there is no
   file or directory name in this entry).

 * If DIR_Name[0] == 0x05, then the actual file name character for this
   byte is 0xE5.

Byte 0xE5 in CP850 is character 'Õ'. So if I try to create file which
starts with 'Õ', then mtools should convert 'Õ' to DOS codepage and if
it is 0xE5 then change it to 0x05.

But mtools does not change 0xE5 to 0x05 which leads to create orphaned
file. Test case for empty FAT filesystem:

$ echo test | mcopy - ::Õtest -i fat
$ mdir :: -i fat
Directory for ::/
No files

It is even worse when you try to rename directory to new name which
would start with 'Õ' character. After running mren the whole directory
which its content is lost:

$ mmd ::test -i fat
$ mdir :: -i fat
Directory for ::/
test         <DIR>     2017-11-17  18:46  test
$ mren ::test ::Õtest -i fat
$ mdir :: -i fat
Directory for ::/
No files

The problem is that mtools does not handle 0xE5 byte correctly and allow
user directly to damage directories entries.

Another program mlabel has exactly same problem:

$ mlabel ::test -i fat
$ mlabel -s ::test -i fat
 Volume label is TEST       
$ mlabel ::Õtest -i fat
$ mlabel -s ::test -i fat
 Volume has no label

In attachment I'm sending fix for this bug.

-- 
Pali Rohár
address@hidden

mtools_0x05.patch
Description: Text Data