Re: [PATCH] _nss_nis_initgroups_dyn: Use struct scratch_buffer [BZ #18023]

[Florian Weimer <fweimer at redhat dot com>]

On 06/25/2018 10:37 PM, DJ Delorie wrote:
> fweimer@redhat.com (Florian Weimer) writes:
> > -      buf = extend_alloca (buf, buflen, 2 * buflen);
> > +      if (!scratch_buffer_grow (&tmpbuf))
> > +	return 1;
>
> The docs say if _grow() fails, the buffer is still free'able.  Could we
> not, or should we, use "break" here so that scratch_buffer_free() is
> called when grow() fails?
>
> The docs (scratch_buffer.h) mentions that the old buffer is freed, but
> that the scratch_buffer is still "in a freeable state" so it's not clear
> if the intention is that you *should* call scratch_buffer_free(), or
> *must*, or *must not*, etc.

You can free the buffer again, but you don't have to.  There is no 
memory leak if you don't.

> >       }
> >   
> > +  scratch_buffer_free (&tmpbuf);
> >     return 1;
> >   }

The point here is not call free if we know it is a no-op.

So I think the code is okay as-is.

> > +	if (!scratch_buffer_grow (&tmpbuf))
> > +	  {
> > +	    status = NSS_STATUS_TRYAGAIN;
> > +	    goto done;
> > +	  }
>
> In this case, going to "done" *does* call scratch_buffer_free().  At
> least we should be consistent within a given file ;-)

Here we call the entire cleanup sequence, which happens to include 
scratch_buffer_free as well, so the situation is different.

I hope this clarifies why things are the way they are.

Thanks,
Florian