netdev - Re: [RFC V2 PATCH] rtnetlink: Fix problem with buffer allocation

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Date:	Wed, 15 Feb 2012 09:08:14 -0500
From:	Thomas Graf <tgraf@...radead.org>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Greg Rose <gregory.v.rose@...el.com>, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [RFC V2 PATCH] rtnetlink: Fix problem with buffer allocation

On Tue, Feb 14, 2012 at 09:13:13PM +0000, Ben Hutchings wrote:
> > +		struct rtattr *ext_req;
> > +		u32 *ext_req_data;
> > +		req = (struct rtnl_req_extended *)cb->nlh;
> > +		ext_req = (struct rtattr *)&req->ext;
> > +		if (ext_req->rta_type == IFLA_EXT_MASK) {
> > +			ext_req_data = RTA_DATA(ext_req);
> > +			ext_filter_mask = *ext_req_data;
> > +		}
> > +	}
> 
> We cannot trust a flag to tell us what the length of the message is.  We
> have to check the value of nlmsg_len (which netlink has already
> validated as being within the skb length and >= our declared request
> header length).  I think that makes the flag redundant.
> 
> In fact, I think we should really use nlmsg_parse() here.  That might be
> overkill when there's only a single valid attribute; I don't know.

I think it's worth the effort. You get all the validation for free. And
please use the netlink interface in <net/netlink.h>, the rtattr based
interface has been deprecated a while ago.
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