[PATCH] staging: comedi: verify array index is correct before using it

[Ian Abbott]

On 09/07/2020 11:29, Dan Carpenter wrote:
> This code reads from the array before verifying that "trig" is a valid
> index.  If the index is wildly out of bounds then reading from an
> invalid address could lead to an Oops.
> 
> Fixes: a8c66b684efa ("staging: comedi: addi_apci_1500: rewrite the subdevice support functions")
> Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> ---
>   drivers/staging/comedi/drivers/addi_apci_1500.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/comedi/drivers/addi_apci_1500.c b/drivers/staging/comedi/drivers/addi_apci_1500.c
> index 45ad4ba92f94..689acd69a1b9 100644
> --- a/drivers/staging/comedi/drivers/addi_apci_1500.c
> +++ b/drivers/staging/comedi/drivers/addi_apci_1500.c
> @@ -456,9 +456,9 @@ static int apci1500_di_cfg_trig(struct comedi_device *dev,
>   	unsigned int lo_mask = data[5] << shift;
>   	unsigned int chan_mask = hi_mask | lo_mask;
>   	unsigned int old_mask = (1 << shift) - 1;
> -	unsigned int pm = devpriv->pm[trig] & old_mask;
> -	unsigned int pt = devpriv->pt[trig] & old_mask;
> -	unsigned int pp = devpriv->pp[trig] & old_mask;
> +	unsigned int pm;
> +	unsigned int pt;
> +	unsigned int pp;
>   
>   	if (trig > 1) {
>   		dev_dbg(dev->class_dev,
> @@ -471,6 +471,10 @@ static int apci1500_di_cfg_trig(struct comedi_device *dev,
>   		return -EINVAL;
>   	}
>   
> +	pm = devpriv->pm[trig] & old_mask;
> +	pt = devpriv->pt[trig] & old_mask;
> +	pp = devpriv->pp[trig] & old_mask;
> +
>   	switch (data[2]) {
>   	case COMEDI_DIGITAL_TRIG_DISABLE:
>   		/* clear trigger configuration */
> 

Nice catch!

Reviewed-by: Ian Abbott <abbotti at mev.co.uk>

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