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

[Vivien Didelot]

Hi Florian,

Florian Fainelli <f.fainelli@xxxxxxxxx> writes:

> 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@xxxxxxxxx>

Reviewed-by: Vivien Didelot <vivien.didelot@xxxxxxxxxxxxxxxxxxxx>

Thanks!

        Vivien