linux-kernel - Re: [PATCH net-next] net: dsa: avoid potential use-after-free error

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Date:   Thu, 19 Nov 2020 06:27:50 +0100
From:   Christian Eggers <ceggers@...i.de>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: dsa: avoid potential use-after-free error

On Thursday, 19 November 2020, 00:33:57 CET, Vladimir Oltean wrote:
> On Wed, Nov 18, 2020 at 04:43:35PM +0100, Christian Eggers wrote:
> > If dsa_switch_ops::port_txtstamp() returns false, clone will be freed
> > immediately. Storing the pointer in DSA_SKB_CB(skb)->clone anyway,
> > supports annoying use-after-free bugs.
> 
> Like what?
In my own code. I test for DSA_SKB_CB(skb)->clone in order to determine 
whether a skb has been selected for TX time stamping by 
ksz9477_ptp_port_txtstamp().

> 
> > Signed-off-by: Christian Eggers <ceggers@...i.de>
> > Fixes 146d442c2357 ("net: dsa: Keep a pointer to the skb clone for TX
> > timestamping")
> Not the right format for a Fixes: tag, please try to set up your
> .gitconfig to automate the creation of this tag.
I think you (or somebody else) already noted this. Sorry for postponing.

regards
Christian