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

[Sergei Shtylyov]

On 06/08/2014 01:42 AM, David Rientjes 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.

> > ---
> >   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.

   You can also replace kmalloc()/memcpy() with kmemdup().

WBR, Sergei

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