Re: [Xen-devel] Moving frags and SKBTX_DEV_ZEROCOPY skbs

[David Miller <davem@xxxxxxxxxxxxx>]

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Wed, 14 May 2014 07:23:52 -0700

> On Wed, 2014-05-14 at 14:40 +0100, Zoltan Kiss wrote:
>> Hi,
>> 
>> Recently I've investigated issues around SKBTX_DEV_ZEROCOPY skbs where 
>> the frags list were modified. I came across this function skb_shift(), 
>> which moves frags between skbs. And there are a lot more of such kind, 
>> skb_split or skb_try_coalesce, for example.
>> It could be a dangerous thing if a frag is referenced from an skb which 
>> doesn't have the original destructor_arg, and to avoid that 
>> skb_orphan_frags should be called. Although probably these functions are 
>> not normally touched in usual usecases, I think it would be useful to 
>> review core skb functions proactively and add an skb_orphan_frags 
>> everywhere where the frags could be referenced from other places.
>> Any opinion about this?
> 
> 
> For skb_shift(), it is currently used from tcp stack only, where
> this SKBTX_DEV_ZEROCOPY thing is not used, so I do not think there is a
> bug for the moment.
> 
> I already gave a patch for skb_try_coalesce() : For this one we do not
> wan skb_orphan_frags() overhead. Its simply better in this case to
> abort.

Eric can you please submit this formally?  It is second time I've seen
it posted as RFC :-)

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