netdev - Re: [PATCH net v4] xen-netback: fix fragment detection in checksum setup

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Message-ID: <20131203142838.GH14293@zion.uk.xensource.com>
Date:	Tue, 3 Dec 2013 14:28:38 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Paul Durrant <Paul.Durrant@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Zoltan Kiss <zoltan.kiss@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net v4] xen-netback: fix fragment detection in checksum
 setup

On Tue, Dec 03, 2013 at 02:05:17PM +0000, Paul Durrant wrote:
[...]
> > >
> > > -	header_size = skb->network_header + off + MAX_IPOPTLEN;
> > > -	maybe_pull_tail(skb, header_size);
> > > +	if (!maybe_pull_tail(skb, sizeof(struct iphdr), MAX_IP_HDR_LEN))
> > > +		goto out;
> > > +
> > 
> > I think you need to correctly update err to reflect this failure.
> > Using -EPROTO will wrongly blame frontend while it is backend that's
> > failing to process the packet.
> > 
> 
> But a failure should only occur if the packet is malformed, so that would be a frontend error wouldn't it?
> 

__pskb_pull_tail may fail due to malloc failure.

However the return value of __pskb_pull_tail cannot reflect the wether
the failure is due to malformed packet or OOM. Not sure what's the best
solution here. What's the malformed packet you were talking about?

Wei.

>   Paul
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