linux-kernel - Re: [PATCH] net: dsa: mt7530: fix null pointer dereferencing in port5 setup

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Date:   Fri, 03 Apr 2020 18:09:11 +0000
From:   René van Dorst <opensource@...rst.com>
To:     Chuanhong Guo <gch981213@...il.com>
Cc:     netdev@...r.kernel.org, stable@...r.kernel.org,
        Sean Wang <sean.wang@...iatek.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: mt7530: fix null pointer dereferencing in
 port5 setup

Quoting Chuanhong Guo <gch981213@...il.com>:

Hi Chuanhong,

> The 2nd gmac of mediatek soc ethernet may not be connected to a PHY
> and a phy-handle isn't always available.
> Unfortunately, mt7530 dsa driver assumes that the 2nd gmac is always
> connected to switch port 5 and setup mt7530 according to phy address
> of 2nd gmac node, causing null pointer dereferencing when phy-handle
> isn't defined in dts.

MT7530 tries to detect if 2nd GMAC is using a phy with phy-address 0 or 4.
If so, switch port 5 needs to be setup so that PHY 0 or 4 is available
via port 5 of the switch. Any MAC can talk to PHY 0/4 directly via port 5.
This is also explained in the kernel docs mt7530.txt.

May be there are better way to detect that any node is using phy 0/4 of
the switch.

Funny that I never tested this case that 2nd gmac node exits and is disabled
without using port 5.

Thanks for the fix.

Tested-by: René van Dorst <opensource@...rst.com>

Greats,

René

> This commit fix this setup code by checking return value of
> of_parse_phandle before using it.
>
> Fixes: 38f790a80560 ("net: dsa: mt7530: Add support for port 5")
> Signed-off-by: Chuanhong Guo <gch981213@...il.com>
> Cc: stable@...r.kernel.org
> ---
>
> mt7530 is available as a standalone chip and we should not make it
> tightly coupled with a specific type of ethernet dt binding in the
> first place.
> A proper fix is to replace this port detection logic with a dt
> property under mt7530 node, but that's too much for linux-stable.
>
>  drivers/net/dsa/mt7530.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> index 6e91fe2f4b9a..1d53a4ebcd5a 100644
> --- a/drivers/net/dsa/mt7530.c
> +++ b/drivers/net/dsa/mt7530.c
> @@ -1414,6 +1414,9 @@ mt7530_setup(struct dsa_switch *ds)
>  				continue;
>
>  			phy_node = of_parse_phandle(mac_np, "phy-handle", 0);
> +			if (!phy_node)
> +				continue;
> +
>  			if (phy_node->parent == priv->dev->of_node->parent) {
>  				ret = of_get_phy_mode(mac_np, &interface);
>  				if (ret && ret != -ENODEV)
> --
> 2.25.1