[Info-mtools] iconv and string termination: accessing files by name not working on macOS

[David Elliott]

Hello,

There is a problem when running mtools on macOS, possibly other systems, which 
appears to be caused by a misuse of iconv.

Specifically, in the unix_name function in file_name.c a 13-char buffer is 
used.  This is enough for the 8 + 3 + 1 dot + 1 NUL terminator.  So far so good.

Most names are not the full 12 character string length, yet 12 is 
unconditionally passed to dos_to_wchar.  If iconv use is enabled, the input 
length (len) will be assigned to a local variable (size_t in_len) whose 
reference is passed as the *srcleft (second) parameter to the iconv call.

This means iconv won't stop at the NUL byte, but will attempt to convert all 12 
characters.  This wouldn't be noticeable if iconv converted NUL to NUL, but my 
observation in the debugger is that my iconv is simply skipping over input NUL, 
then converting whatever garbage characters exist after it, up to the limit.

The fix is obvious: use strlen(ans) as the input length.  The NUL gets added to 
the output by existing code and everything works as designed.

This manifests as a simple file not found for commands like `mdir ::/FOOBAR` 
but leads to looping or even a segfault for commands like `mdir -s`, presumably 
because the code is not expecting to fail to list the contents of a 
subdirectory it literally just found.

-David

mtools-iconv.diff
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