On Wed, Sep 28, 2022 at 10:57:55PM +0200, Stefano Brivio wrote:
> On Wed, 28 Sep 2022 14:33:18 +1000
> David Gibson <david(a)gibson.dropbear.id.au> wrote:
> 
> > conf_runas() handles several of the different possible cases for the
> > --runas argument in a slightly odd order.  Although it can parse both
> > numeric UIDs/GIDs and user/group names, it can't parse a numeric UID
> > combined with a group name or vice versa.  That's not obviously useful, but
> > it's slightly surprising gap to have.
> 
> Ah, actually, I had noticed that: I usually type my UID as number, but
> I can't remember GIDs... then I had half a mind of "fixing" that, and
> never got to it.
> 
> > [...]
> >
> > +++ b/conf.c
> > @@ -859,46 +859,50 @@ dns6:
> >   *
> >   * Return: 0 on success, negative error code on failure
> >   */
> > -static int conf_runas(const char *opt, unsigned int *uid, unsigned int *gid)
> > +static int conf_runas(char *opt, unsigned int *uid, unsigned int *gid)
> 
> While I like your approach better than the existing one, I see one
> detail that, albeit minor, might drive somebody mad: if the UID is
> valid, but the GID isn't, we go back to conf_ugid():
> 
> 		if (ret)
> 			err("Invalid --runas option: %s", runas);
> 
> and print the UID part, only, because we cut before the separator.

Urgh, right.  This is why having worked a bit with Rust and Go, I'm
really coming to hate C-style strings: even really rudimentary parsing
usually requires either allocation & copies or modifying logically
read-only inputs.

> Perhaps we could simply put the separator back before returning
> -EINVAL (instead of copying the buffer) -- we just have zero or one
> occurrences of ':'.

That would work, although making sure we do that on every exit path
looks messier than I'd like.  I went with a different approach of
removing that message from the caller, and instead printing more
specific messages for each of the cases within conf_runas().  A little
more involved, but I think gives a marginally better UX overall.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson