Behaviour of .so differs between mandoc and groff

[Alexis]

Hi all,

On my Gentoo system, awk.1 simply contains an .so request whose 
argument is the man page for the actual awk implementation in use, 
i.e. just:

   .so gawk.1

However, although this works when using man-db, it doesn't when 
one is using mandoc instead, as on my system. Instead of gawk.1 
being sourced, processed and displayed, i get output along the 
lines of:

   ()                                    ()
   
   
   See the file gawk.1.


   ()

However, if i change the request in awk.1 to:

   .so man1/gawk.1

then everything works as expected.

The example in the entry for .so in mandoc_roff(7) is what led me 
to try the preceding, but there's no further indication that the 
requirement for a leading section directory is consciously 
different from any other roff implementation, or from groff in 
particular. A comment in roff_so() in mandoc/roff.c[a] says:

   /*
   /* Handle `so'.  Be EXTREMELY careful, as we shouldn't be
    * opening anything that's not in our cwd or anything beneath
    * it.  Thus, explicitly disallow traversing up the 
    file-system
    * or using absolute paths.
    */

i couldn't find any discussion about .so in the mandoc TODO 
list[b].

i've no idea what the 'correct' behaviour 'should' be, from 
whatever perspective (historical / security / groff-compatibility 
/ etc.), so am cross-posting to what i believe to be the relevant 
lists.


Alexis.

[a] 
https://cvsweb.bsd.lv/mandoc/roff.c?rev=1.395&content-type=text/x-cvsweb-markup

[b] 
https://cvsweb.bsd.lv/mandoc/TODO?rev=1.327&content-type=text/x-cvsweb-markup