netdev - Re: [PATCH net-next] can: sja1000: fix use after free in ems_pcmcia_add

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Message-ID: <72ed48e9-0659-78f9-1b31-be54b118ab76@hartkopp.net>
Date:   Tue, 23 Nov 2021 21:42:12 +0100
From:   Oliver Hartkopp <socketcan@...tkopp.net>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Wolfgang Grandegger <wg@...ndegger.com>
Cc:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Leon Romanovsky <leon@...nel.org>, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net-next] can: sja1000: fix use after free in
 ems_pcmcia_add_card()

Hello Dan,

On 22.11.21 08:56, Dan Carpenter wrote:
> In the original code if ems_pcmcia_check_chan() returned false then
> it called free_sja1000dev(dev) but did not set the error code or jump
> to the clean up code.  This frees "dev" and leads to a use after free.
> 
> I flipped the ems_pcmcia_check_chan() check around to make the error
> handling more consistent and readable.  That lets us pull the rest of
> the code in one tab.
> 
> Fixes: fd734c6f25ae ("can/sja1000: add driver for EMS PCMCIA card")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

I do not think, that you are fixing something here.

The loop

for (i = 0; i < EMS_PCMCIA_MAX_CHAN; i++) { ...

checks with

if (ems_pcmcia_check_chan(priv))

whether this channel is 'available' or not.

As this hardware could come with only ONE channel it is just wrong to 
tag a missing channel as error and finally kill the entire setup process 
(including the potentially working channel we already initialized).

So thanks for the patch but NACK ;-)

Best regards,
Oliver


> ---
>   drivers/net/can/sja1000/ems_pcmcia.c | 44 +++++++++++++++-------------
>   1 file changed, 23 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/net/can/sja1000/ems_pcmcia.c b/drivers/net/can/sja1000/ems_pcmcia.c
> index e21b169c14c0..271fe9444827 100644
> --- a/drivers/net/can/sja1000/ems_pcmcia.c
> +++ b/drivers/net/can/sja1000/ems_pcmcia.c
> @@ -210,28 +210,30 @@ static int ems_pcmcia_add_card(struct pcmcia_device *pdev, unsigned long base)
>   			(i * EMS_PCMCIA_CAN_CTRL_SIZE);
>   
>   		/* Check if channel is present */
> -		if (ems_pcmcia_check_chan(priv)) {
> -			priv->read_reg  = ems_pcmcia_read_reg;
> -			priv->write_reg = ems_pcmcia_write_reg;
> -			priv->can.clock.freq = EMS_PCMCIA_CAN_CLOCK;
> -			priv->ocr = EMS_PCMCIA_OCR;
> -			priv->cdr = EMS_PCMCIA_CDR;
> -			priv->flags |= SJA1000_CUSTOM_IRQ_HANDLER;
> -
> -			/* Register SJA1000 device */
> -			err = register_sja1000dev(dev);
> -			if (err) {
> -				free_sja1000dev(dev);
> -				goto failure_cleanup;
> -			}
> -
> -			card->channels++;
> -
> -			printk(KERN_INFO "%s: registered %s on channel "
> -			       "#%d at 0x%p, irq %d\n", DRV_NAME, dev->name,
> -			       i, priv->reg_base, dev->irq);
> -		} else
> +		if (!ems_pcmcia_check_chan(priv)) {
> +			err = -EINVAL;
>   			free_sja1000dev(dev);
> +			goto failure_cleanup;
> +		}
> +		priv->read_reg  = ems_pcmcia_read_reg;
> +		priv->write_reg = ems_pcmcia_write_reg;
> +		priv->can.clock.freq = EMS_PCMCIA_CAN_CLOCK;
> +		priv->ocr = EMS_PCMCIA_OCR;
> +		priv->cdr = EMS_PCMCIA_CDR;
> +		priv->flags |= SJA1000_CUSTOM_IRQ_HANDLER;
> +
> +		/* Register SJA1000 device */
> +		err = register_sja1000dev(dev);
> +		if (err) {
> +			free_sja1000dev(dev);
> +			goto failure_cleanup;
> +		}
> +
> +		card->channels++;
> +
> +		printk(KERN_INFO "%s: registered %s on channel "
> +		       "#%d at 0x%p, irq %d\n", DRV_NAME, dev->name,
> +		       i, priv->reg_base, dev->irq);
>   	}
>   
>   	err = request_irq(dev->irq, &ems_pcmcia_interrupt, IRQF_SHARED,
>