Re: [PATCH v2] dns_resolver: assure that dns_query() result is null-terminated

[Manuel Schoelling <manuel.schoelling@gmx.de>]

On Sa, 2014-06-07 at 14:42 -0700, David Rientjes wrote:
> On Sat, 7 Jun 2014, Manuel Schölling wrote:
> 
> > dns_query() credulously assumes that keys are null-terminated and
> > returns a copy of a memory block that is off by one.
> 
> No sign-off?  Please read Documentation/SubmittingPatches.
It's just not my day today.
Sorry, I forgot about the sign-off.

> > ---
> >  net/dns_resolver/dns_query.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
> > index e7b6d53..84871a2 100644
> > --- a/net/dns_resolver/dns_query.c
> > +++ b/net/dns_resolver/dns_query.c
> > @@ -145,11 +145,11 @@ int dns_query(const char *type, const char *name, size_t namelen,
> >  	len = upayload->datalen;
> >  
> >  	ret = -ENOMEM;
> > -	*_result = kmalloc(len + 1, GFP_KERNEL);
> > +	*_result = kzalloc(len + 1, GFP_KERNEL);
> >  	if (!*_result)
> >  		goto put;
> >  
> > -	memcpy(*_result, upayload->data, len + 1);
> > +	memcpy(*_result, upayload->data, len);
> >  	if (_expiry)
> >  		*_expiry = rkey->expiry;
> >  
> 
> kzalloc() would be unnecessary overhead (zeroing definitely comes with a 
> cost) if you're going to copy to the memory immediately afterwards.  Just 
> leave the kmalloc(), do the memcpy() and explicitly zero terminate it 
> _result.

Using kzalloc() was suggested of a developer on IRC (#kernelnewbies) but
if you prefer kmalloc, that's ok, too.
I'll send you a corrected patch in a second.