netdev - Re: Moving frags and SKBTX_DEV

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Message-ID: <1400089943.7973.105.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 14 May 2014 10:52:23 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	zoltan.kiss@...rix.com, netdev@...r.kernel.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org
Subject: Re: Moving frags and SKBTX_DEV_ZEROCOPY skbs

On Wed, 2014-05-14 at 13:42 -0400, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> 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 :-)

Sure, I was kind of waiting to make sure it was needed.

It looks like it is ;)


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