Re: [PATCH 1/4] conf: Copy up to MAXDNSRCH - 1 bytes, not MAXDNSRCH

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Jun 27, 2024 at 09:27:01AM +0200, Stefano Brivio wrote:
> On Thu, 27 Jun 2024 10:45:28 +1000
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > On Thu, Jun 27, 2024 at 01:45:33AM +0200, Stefano Brivio wrote:
> > > Spotted by Coverity just recently. Not that it really matters as
> > > MAXDNSRCH always appears to be defined as 1025, while a full domain
> > > name can have up to 253 characters: it would be a bit pointless to
> > > have a longer search domain.
> > > 
> > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>  
> > 
> > Hm.  So, IIRC strncpy() won't \0 terminate in the case where it
> > truncates.  I guess we'll get away with that here since we expect
> > c->dns_search to be filled with \0 before hand.  That's... more
> > fragile than ideal, though.
> 
> Well, we know we start from a zero-initialised area, that's by design,
> it's not that we get away with it. Without that consideration not many
> things would work in this function.

That's a fair point.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> Are you suggesting to use snprintf()? It looks a bit pedantic to me but
> I'm fine with it. Otherwise, feel free to post a patch fixing it in a
> way you feel it's ideal...
> 
> > > ---
> > >  conf.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/conf.c b/conf.c
> > > index e1f5422..9e47e9a 100644
> > > --- a/conf.c
> > > +++ b/conf.c
> > > @@ -453,7 +453,7 @@ static void get_dns(struct ctx *c)
> > >  			while (s - c->dns_search < ARRAY_SIZE(c->dns_search) - 1
> > >  			       /* cppcheck-suppress strtokCalled */
> > >  			       && (p = strtok(NULL, " \t"))) {
> > > -				strncpy(s->n, p, sizeof(c->dns_search[0]));
> > > +				strncpy(s->n, p, sizeof(c->dns_search[0]) - 1);
> > >  				s++;
> > >  				*s->n = 0;
> > >  			}  
> > 
> 

-- 
David Gibson (he or they)	| 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

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