Re: [PATCH 3.2-3.12] skbuff: skb_segment: orphan frags before copying

[Luis Henriques <luis.henriques@canonical.com>]

On Fri, Jun 06, 2014 at 05:09:28PM +0100, Ben Hutchings wrote:
> From: "Michael S. Tsirkin" <mst@redhat.com>
> 
> commit 1fd819ecb90cc9b822cd84d3056ddba315d3340f upstream.
> 
> skb_segment copies frags around, so we need
> to copy them carefully to avoid accessing
> user memory after reporting completion to userspace
> through a callback.
> 
> skb_segment doesn't normally happen on datapath:
> TSO needs to be disabled - so disabling zero copy
> in this case does not look like a big deal.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> [bwh: Backported to 3.2.  As skb_segment() only supports page-frags *or* a
>  frag list, there is no need for the additional frag_skb pointer or the
>  preparatory renaming.]
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
> This is what I used in Debian for 3.2, and I believe it applies to all
> stable branches up to 3.12 inclusive.
> 
> For branches older than 3.6, this requires cherry-picking commit
> a353e0ce0fd4 ('skbuff: add an api to orphan frags').  To avoid breaking
> OOT builds of openvswitch, which will use skb_orphan_frags() if
> available, it is also necessary to cherry-pick commit dcc0fb782b3a
> ('skbuff: export skb_copy_ubufs').
> 
> Ben.
> 

Thanks Ben, I'll queue it for the 3.11 kernel.

Cheers,
--
Luís

> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -2701,6 +2701,9 @@ struct sk_buff *skb_segment(struct sk_bu
>  						 skb_put(nskb, hsize), hsize);
>  
>  		while (pos < offset + len && i < nfrags) {
> +			if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
> +				goto err;
> +
>  			*frag = skb_shinfo(skb)->frags[i];
>  			__skb_frag_ref(frag);
>  			size = skb_frag_size(frag);
> 
> -- 
> Ben Hutchings
> You can't have everything.  Where would you put it?