Root directory being a junction fools realpath()

[Corinna Vinschen]

On Feb 14 12:56, David Macek via Cygwin-developers wrote:
> Greetings.
> 
> I think I found a way to fool Cygwin into misplacing its root
> directory. Given recent Cygwin with GCC and a simple test program:
> 
> ```
> #include <stdio.h>
> #include <limits.h>
> #include <stdlib.h>
> int main() {
> char real[PATH_MAX];
> realpath("/", real);
> printf("/ -> %s\n", real);
> return 0;
> }
> ```
> 
> ... compiled with:
> 
> $ gcc -D_DEFAULT_SOURCE -o new.exe -Wall -Wextra -std=c11 new.c
> 
> ... and my set-up with a junction (`mklink /j link target`) realpath()
> result is dependent on which path I use to invoke the Cygwin root
> process:
> 
> > dir C:\ | findstr cygwin64
> 10. 02. 2021  12:13    <DIR>          cygwin64
> 
> > dir D:\ | findstr cygwin64
> 14. 02. 2021  12:19    <JUNCTION>     cygwin64 [C:\cygwin64]
> 
> > C:\cygwin64\bin\bash -lc /cygdrive/w/new
> / -> /
> 
> > D:\cygwin64\bin\bash -lc /cygdrive/w/new
> / -> /cygdrive/c/cygwin64

This isn't realpath's fault.  You're circumventing the mount point
handling which is automated in terms of /, depending on the path
returned from GetModuleFileNameW for the Cygwin DLL.  Since you're
calling D:\cygwin64\bin\bash the dir returned from GetModuleFileNameW is
D:\cygwin64\bin, thus root is D:\cygwin64.

However, junctions are treated as symlinks in Cygwin.  Thus the result
you see above.


Corinna