linux-kernel - Re: [PATCH net] net: dsa: Fix stale cpu_switch reference after unbind then bind

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Date:   Sun, 04 Jun 2017 22:57:40 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     f.fainelli@...il.com
Cc:     netdev@...r.kernel.org, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: Fix stale cpu_switch reference after
 unbind then bind

From: Florian Fainelli <f.fainelli@...il.com>
Date: Fri,  2 Jun 2017 22:05:23 -0700

> Commit 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
> replaced the use of dst->ds[0] with dst->cpu_switch since that is
> functionally equivalent, however, we can now run into an use after free
> scenario after unbinding then rebinding the switch driver.
> 
> The use after free happens because we do correctly initialize
> dst->cpu_switch the first time we probe in dsa_cpu_parse(), then we
> unbind the driver: dsa_dst_unapply() is called, and we rebind again.
> dst->cpu_switch now points to a freed "ds" structure, and so when we
> finally dereference it in dsa_cpu_port_ethtool_setup(), we oops.
> 
> To fix this, simply set dst->cpu_switch to NULL in dsa_dst_unapply()
> which guarantees that we always correctly re-assign dst->cpu_switch in
> dsa_cpu_parse().
> 
> Fixes: 9520ed8fb841 ("net: dsa: use cpu_switch instead of ds[0]")
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>

Applied and queued up for -stable, thanks.