Re: luasocket: segfault with dns.toip and suggested fix

[Brian Murphy <brian@...>]

Diego Nehab wrote:

> Hi Bill,
>
> > As a fix I've simply put a test around the above code like this:
> >
> >    if (alias) {        while (*alias) {
> >        lua_pushnumber(L, i);
> >        lua_pushstring(L, *alias);
> >        lua_settable(L, -3);
> >        i++; alias++;
> >        }
> >    }
> >
> > The above fix works but I'm not sure if it is the best solution within
> > the design of luasocket; perhaps a fix deeper in the socket hierarchy
> > (e.g. usocket.c) would be better.
>
>
> Seems hard to fix it within usocket.c. I don't object to your approach 
> and
> I am happy to prevent LuaSocket from crashing anywhere possible.
>
> Thanks,
> Diego.
Now that I see this I remember another similar error.

gethostbyname and gethostbyaddr return a pointer to NULL when they fail
and (should) set h_errno to something. My operating system does the first
but forgets to set h_errno.
sock_gethostbyaddr and sock_gethostbyname use 0 as a success return
code and the routine returned to uses the NULL pointer  and blows up.

The line:
else return h_errno;

should probably at least contain an assertion that h_errno != IO_DONE
to alert possible porters to the real cause of their problems as soon
as possible.

/Brian