Re: [patch] gpiolib: potential oops on failure path

walter harms
2016-06-17T09:28:33Z

Am 17.06.2016 11:15, schrieb Dan Carpenter:
> If anon_inode_getfd() fails then "i" is set to GPIOHANDLES_MAX. It
> means that we will read beyond the end of the array and dereference an
> invalid pointer.
>
> Fixes: d7c51b47ac11 ('gpio: userspace ABI for reading/writing GPIO lines')
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 8b3db59..8578b7f 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -495,6 +495,8 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
> return 0;
>
> out_free_descs:
> + if (i = GPIOHANDLES_MAX)
> + i--;
> for (; i >= 0; i--)
> gpiod_free(lh->descs[i]);
> kfree(lh->label);

Since we have already noticed that programmes are bad at counting backwards
is it possible to change the loop into counting up ?

btw: if lh->descs[i] is initialized to NULL it would be more robust just to free everything like:

for(i=0;i< GPIOHANDLES_MAX; i++)
gpiod_free(lh->descs[i]);

just my two cents,

re,
wh