netdev - Re: [PATCH net] net/sched: act_pedit: really ensure the skb is writable

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Message-ID: <20220504083334.1b7a98e3@kernel.org>
Date:   Wed, 4 May 2022 08:33:34 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, netdev@...r.kernel.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH net] net/sched: act_pedit: really ensure the skb is
 writable

On Wed, 04 May 2022 17:11:25 +0200 Paolo Abeni wrote:
> > For testing stuff like this would it be possible to inject packets
> > with no headers pulled and frags in pages we marked read-only?
> > We can teach netdevsim to do it.  
> 
> We additionally need to ensure that the crafted packets are cloned,
> otherwise the current code is AFAICS fine.

Depends whether skb frags are writable, or not. Or to put it differently
why does skb_cow_data() exist and does what it does.