[PATCH 2/3] tests: Don't pass INT_MAX to virFileReadAll()

[Peter Krempa]

On Mon, Jun 14, 2021 at 14:30:26 +0200, Michal Prívozník wrote:
> On 6/14/21 2:26 PM, Peter Krempa wrote:
> > On Mon, Jun 14, 2021 at 14:14:47 +0200, Michal Prívozník wrote:
> >> On 6/14/21 1:31 PM, Tim Wiederhake wrote:
> >>> On Mon, 2021-06-14 at 13:06 +0200, Michal Privoznik wrote:
> >>>> In a few occasions in tests we pass INT_MAX to
> >>>> virFileReadLimFD(). This is not safe because virFileReadAll()
> >>>> will call virFileReadLimFD() under the hood which takes the limit
> >>>> and adds 1 to it.
> >>>
> >>> Calling virFileReadAll with "INT_MAX - 1" looks funny. Is it possible
> >>> to check for "maxlen >= INT_MAX" in virFileReadLimFD instead?
> >>
> >> Actually, I don't understand why we need to add 1 in the first place.
> >> I'll push the other two patches and send v2 for this that removes the +1.
> > 
> > It's so that it guarantees that a file of 'maxlen' length is read
> > completely and the terminating '\0' is in the resulting string.
> > 
> > Removing the '+ 1' would change this kind of semantics, which may
> > require audit of all callers.
> > 
> 
> I'm not sure that's correct behaviour. I mean, if I specify that the
> limit should be X, then at the most X bytes should be read, not X+1.
> 
> Also, virFileReadLimFD() uses saferead_lim() which upon successful
> return makes sure the returned string is properly terminated.

saferead_lim indeed terminates the string properly. virFileReadLimFD
uses the '+ 1' to see whether there are exactly "maxlen" chars in the
file or potentially more than that. That's why it actually reads 1 more
than the requested maximum.

Whether that makes sense is obviously questionable and will require
audit of all callers