Subject: Re: [PATCH nf 2/2] netfilter: nf_tables: add clone interface to expression operations

From: Pablo Neira Ayuso <[email-masked]>
Date: Tue, 10 Nov 2015 19:39:05 +0100

On Tue, Nov 10, 2015 at 06:30:34PM +0000, Patrick McHardy wrote:
> On 10.11, Pablo Neira Ayuso wrote:
> > With the conversion of the counter expressions to make it percpu, we
> > need to clone the percpu memory area, otherwise we crash when using
> > counters from flow tables.
> > 
> > Signed-off-by: Pablo Neira Ayuso <[email-masked]>
> > ---
> >  include/net/netfilter/nf_tables.h | 16 +++++++++++--
> >  net/netfilter/nft_counter.c       | 49 ++++++++++++++++++++++++++++++++-------
> >  net/netfilter/nft_dynset.c        |  5 ++--
> >  3 files changed, 58 insertions(+), 12 deletions(-)
> > 
> > diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
> > index c9149cc..c186457 100644
> > --- a/include/net/netfilter/nf_tables.h
> > +++ b/include/net/netfilter/nf_tables.h
> > @@ -630,6 +630,8 @@ struct nft_expr_ops {
> >  	int				(*validate)(const struct nft_ctx *ctx,
> >  						    const struct nft_expr *expr,
> >  						    const struct nft_data **data);
> > +	int				(*clone)(struct nft_expr *dst,
> > +						 const struct nft_expr *src);
> 
> The functions and data needed during runtime are deliberately kept together
> at the beginning of the structure to avoid having to read the entire thing.
> So I'd say this shoud go after ->eval().

OK, I'll place this after ->eval.

> > @@ -660,10 +662,20 @@ void nft_expr_destroy(const struct nft_ctx *ctx, struct nft_expr *expr);
> >  int nft_expr_dump(struct sk_buff *skb, unsigned int attr,
> >  		  const struct nft_expr *expr);
> >  
> > -static inline void nft_expr_clone(struct nft_expr *dst, struct nft_expr *src)
> > +static inline int nft_expr_clone(struct nft_expr *dst, struct nft_expr *src)
> >  {
> > +	int err;
> > +
> >  	__module_get(src->ops->type->owner);
> > -	memcpy(dst, src, src->ops->size);
> > +	if (src->ops->clone) {
> > +		memcpy(dst, src, sizeof(*src));
> 
> Why copy if we clone? The function should do a full initialization if it is
> present I would say.

This is not copying the variable length data area of the expression,
just the expression head.

> > +		err = src->ops->clone(dst, src);
> > +		if (err < 0)
> > +			return err;
> > +	} else {
> > +		memcpy(dst, src, src->ops->size);
> > +	}
> > +	return 0;
> >  }
> >