netdev - Re: [PATCH net-next 1/3] net: fix possible user-after-free in skb_ext

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Message-ID: <20181220193242.fjtjhh5awp5zu7dy@breakpoint.cc>
Date:   Thu, 20 Dec 2018 20:32:42 +0100
From:   Florian Westphal <fw@...len.de>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 1/3] net: fix possible user-after-free in
 skb_ext_add()

Paolo Abeni <pabeni@...hat.com> wrote:
> On cow we can free the old extension: we must avoid dereferencing
> such extension after skb_ext_maybe_cow(). Since 'new' contents
> are always equal to 'old' after the copy, we can fix the above
> accessing the relevant data using 'new'.

Yep, this is indeed possible when two clones of same skb
have skb_ext_add() invoked at the same time from two different
context.

Thanks for spotting this.

Acked-by: Florian Westphal <fw@...len.de>