linux-kernel - Re: [PATCH net] net: phy: sfp: Prevent NULL deference of socket

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Date:   Mon, 17 Sep 2018 10:30:52 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: phy: sfp: Prevent NULL deference of socket_ops

On 09/15/2018 12:32 AM, Russell King - ARM Linux wrote:
> On Fri, Sep 14, 2018 at 04:01:31PM -0700, Florian Fainelli wrote:
>> In case we have specified a SFP and an I2C phandle in the Device Tree,
>> but we somehow failed to look up the I2C adapter (e.g: the driver is not
>> enabled), we will leave dangling socket_ops, and the sfp_bus will still
>> have been registered. We can then observe NULL pointer dereferences
>> while doing ethtool -m:
>>
>> [   20.218613] Unable to handle kernel NULL pointer dereference at virtual address 00000008
>> [   20.226977] pgd = (ptrval)
>> [   20.229785] [00000008] *pgd=7c400831, *pte=00000000, *ppte=00000000
>> [   20.236274] Internal error: Oops: 17 [#1] SMP ARM
>> [   20.241122] Modules linked in:
>> [   20.244278] CPU: 0 PID: 1480 Comm: ethtool Not tainted 4.19.0-rc3 #138
>> [   20.251013] Hardware name: Broadcom Northstar Plus SoC
>> [   20.256316] PC is at sfp_get_module_info+0x8/0x10
>> [   20.261172] LR is at dev_ethtool+0x218c/0x2afc
>>
>> Specifically guard against that.
> 
> The other alternative to this would be to only set ndev->sfp_bus when
> the bus moves to registered state, which would probably be a saner
> alternative than to add an additional layer of tests.  IOW:

Indeed, your patch works for me:

Tested-by: Florian Fainelli <f.fainelli@...il.com>

> 
>  drivers/net/phy/sfp-bus.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/sfp-bus.c b/drivers/net/phy/sfp-bus.c
> index 48ca980f5c96..c4c2b5269216 100644
> --- a/drivers/net/phy/sfp-bus.c
> +++ b/drivers/net/phy/sfp-bus.c
> @@ -362,6 +362,7 @@ static int sfp_register_bus(struct sfp_bus *bus)
>  	}
>  	if (bus->started)
>  		bus->socket_ops->start(bus->sfp);
> +	bus->netdev->sfp_bus = bus;
>  	bus->registered = true;
>  	return 0;
>  }
> @@ -370,6 +371,7 @@ static void sfp_unregister_bus(struct sfp_bus *bus)
>  {
>  	const struct sfp_upstream_ops *ops = bus->upstream_ops;
>  
> +	bus->netdev->sfp_bus = NULL;
>  	if (bus->registered) {
>  		if (bus->started)
>  			bus->socket_ops->stop(bus->sfp);
> @@ -451,7 +453,6 @@ static void sfp_upstream_clear(struct sfp_bus *bus)
>  {
>  	bus->upstream_ops = NULL;
>  	bus->upstream = NULL;
> -	bus->netdev->sfp_bus = NULL;
>  	bus->netdev = NULL;
>  }
>  
> @@ -480,7 +481,6 @@ struct sfp_bus *sfp_register_upstream(struct fwnode_handle *fwnode,
>  		bus->upstream_ops = ops;
>  		bus->upstream = upstream;
>  		bus->netdev = ndev;
> -		ndev->sfp_bus = bus;
>  
>  		if (bus->sfp) {
>  			ret = sfp_register_bus(bus);
> 


-- 
Florian