linux-kernel - Re: [PATCH net-next v2] net: dsa: avoid potential use-after-free error

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Message-ID: <20201120125921.1cb76a12@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 20 Nov 2020 12:59:21 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Christian Eggers <ceggers@...i.de>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] net: dsa: avoid potential use-after-free
 error

On Fri, 20 Nov 2020 20:01:49 +0200 Vladimir Oltean wrote:
> On Thu, Nov 19, 2020 at 12:09:06PM +0100, Christian Eggers wrote:
> > If dsa_switch_ops::port_txtstamp() returns false, clone will be freed
> > immediately. Shouldn't store a pointer to freed memory.
> > 
> > Signed-off-by: Christian Eggers <ceggers@...i.de>
> > Fixes: 146d442c2357 ("net: dsa: Keep a pointer to the skb clone for TX timestamping")
> > ---  
> 
> IMO this is one of the cases to which the following from
> Documentation/process/stable-kernel-rules.rst does not apply:
> 
>  - It must fix a real bug that bothers people (not a, "This could be a
>    problem..." type thing).
> 
> Therefore, specifying "net-next" as the target tree here as opposed to
> "net" is the correct choice.

The commit message doesn't really explain what happens after.

Is the dangling pointer ever accessed?