Re: [PATCH net 1/1] net: ppp: fix creating PPP pass and active filters

[Varka Bhadram <varkabhadram@gmail.com>]

On Sunday 13 July 2014 06:29 PM, Christoph Schulz wrote:
> From: Christoph Schulz <develop@kristov.de>
>
> Commit 568f194e8bd16c353ad50f9ab95d98b20578a39d ("net: ppp: use
> sk_unattached_filter api") inadvertently changed the logic when setting
> PPP pass and active filters. This applies to both the generic PPP subsystem
> implemented by drivers/net/ppp/ppp_generic.c and the ISDN PPP subsystem
> implemented by drivers/isdn/i4l/isdn_ppp.c. The original code in ppp_ioctl()
> (or isdn_ppp_ioctl(), resp.) handling PPPIOCSPASS and PPPIOCSACTIVE allowed to
> remove a pass/active filter previously set by using a filter of length zero.
> However, with the new code this is not possible anymore as this case is not
> explicitly checked for, which leads to passing NULL as a filter to
> sk_unattached_filter_create(). This results in returning EINVAL to the caller.
>
> Additionally, the variables ppp->pass_filter and ppp->active_filter (or
> is->pass_filter and is->active_filter, resp.) are not reset to NULL, although
> the filters they point to may have been destroyed by
> sk_unattached_filter_destroy(), so in this EINVAL case dangling pointers are
> left behind (provided the pointers were previously non-NULL).
>
> This patch corrects both problems by checking whether the filter passed is
> empty or non-empty, and prevents sk_unattached_filter_create() from being
> called in the first case. Moreover, the pointers are always reset to NULL
> as soon as sk_unattached_filter_destroy() returns.
>
> Signed-off-by: Christoph Schulz <develop@kristov.de>
> ---
> diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
> index 61ac632..cd2f4c3 100644
> --- a/drivers/isdn/i4l/isdn_ppp.c
> +++ b/drivers/isdn/i4l/isdn_ppp.c
> @@ -644,9 +644,15 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
>   		fprog.len = len;
>   		fprog.filter = code;
>   
> -		if (is->pass_filter)
> +		if (is->pass_filter) {
>   			sk_unattached_filter_destroy(is->pass_filter);
> -		err = sk_unattached_filter_create(&is->pass_filter, &fprog);
> +			is->pass_filter = NULL;
> +		}
> +		if (fprog.filter != NULL)
> +			err = sk_unattached_filter_create(&is->pass_filter,
> +							  &fprog);
> +		else
> +			err = 0;
>   		kfree(code);
>   
>   		return err;
> @@ -663,9 +669,15 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
>   		fprog.len = len;
>   		fprog.filter = code;
>   
> -		if (is->active_filter)
> +		if (is->active_filter) {
>   			sk_unattached_filter_destroy(is->active_filter);
> -		err = sk_unattached_filter_create(&is->active_filter, &fprog);
> +			is->active_filter = NULL;
> +		}
> +		if (fprog.filter != NULL)
> +			err = sk_unattached_filter_create(&is->active_filter,
> +							  &fprog);
> +		else
> +			err = 0;
>   		kfree(code);
>   
>   		return err;
> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index 91d6c12..d0f6f93 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -763,10 +763,15 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>   			};
>   
>   			ppp_lock(ppp);
> -			if (ppp->pass_filter)
> +			if (ppp->pass_filter) {
>   				sk_unattached_filter_destroy(ppp->pass_filter);
> -			err = sk_unattached_filter_create(&ppp->pass_filter,
> -							  &fprog);
> +				ppp->pass_filter = NULL;
> +			}
> +			if (fprog.filter != NULL)
> +				err = sk_unattached_filter_create(&ppp->pass_filter,
> +								  &fprog);
> +			else
> +				err = 0;
>   			kfree(code);
>   			ppp_unlock(ppp);
>   		}
> @@ -784,10 +789,15 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>   			};
>   
>   			ppp_lock(ppp);
> -			if (ppp->active_filter)
> +			if (ppp->active_filter) {
>   				sk_unattached_filter_destroy(ppp->active_filter);
> -			err = sk_unattached_filter_create(&ppp->active_filter,
> -							  &fprog);
> +				ppp->active_filter = NULL;
> +			}
> +			if (fprog.filter != NULL)
> +				err = sk_unattached_filter_create(&ppp->active_filter,
> +								  &fprog);
> +			else
> +				err = 0;
>   			kfree(code);
>   			ppp_unlock(ppp);
>   		}
> --
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checkpatch warnings on this patch

-- 
Regards,
Varka Bhadram