Weird issue with file permissions

[Ken Brown]

On 7/2/2022 12:16 PM, Lavrentiev, Anton (NIH/NLM/NCBI) [C] wrote:
> I forgot to mention that my "umask" is the standard 022...
> 
> The man page says that for directories with the ACLs, it is ignored.
> 
> So in my code bind() wouldn't have created the socket with 0777, and
> that's fine!  Which is why I call fchmod() to fix the permissions up,
> and THAT does not work.  BTW, should I have called chmod() instead (which
> is what the command line chmod does), the permissions would have been
> set correctly on the socket file, but fchmod() would have misreported
> them again (this time looks like a carryover from an earlier umask(0))!

I was focused on ACLs in my earlier responses and didn't think hard enough about 
what your test program was actually doing.  But you seem to be assuming that 
calling fchmod on a socket descriptor should affect the permissions on the 
socket file (assuming the socket is bound).  Is that documented anywhere?  POSIX 
says that the behavior of fchmod on a socket descriptor is unspecified 
(https://pubs.opengroup.org/onlinepubs/9699919799/functions/fchmod.html#tag_16_119).

Ken