[5/5] gtp: let userspace handle packets for invalid tunnels

Submitted by Andreas Schultz on Jan. 24, 2017, 5:24 p.m.

Details

Message ID 20170124172402.12096-6-aschultz@tpip.net
State New
Headers show

Commit Message

Andreas Schultz Jan. 24, 2017, 5:24 p.m.
enable userspace to send error replies for invalid tunnels

Signed-off-by: Andreas Schultz <aschultz@tpip.net>
---
 drivers/net/gtp.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Pablo Neira Jan. 24, 2017, 7:03 p.m.
Hi Andreas,

On Tue, Jan 24, 2017 at 06:24:02PM +0100, Andreas Schultz wrote:
> enable userspace to send error replies for invalid tunnels
> 
> Signed-off-by: Andreas Schultz <aschultz@tpip.net>
> ---
>  drivers/net/gtp.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
> index 912721e..c607333 100644
> --- a/drivers/net/gtp.c
> +++ b/drivers/net/gtp.c
> @@ -198,12 +198,12 @@ static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb,
>  	pctx = gtp0_pdp_find(gtp, be64_to_cpu(gtp0->tid));
>  	if (!pctx) {
>  		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
> -		return -1;
> +		return 1;
>  	}
>  
>  	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
>  		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
> -		return -1;
> +		return 1;

So userspace gets the packet that we cannot forward. I guess your
userspace codebase performs this sanity checks again so you can send
the appropriate error reply?

>  	}
>  
>  	/* Get rid of the GTP + UDP headers. */
> @@ -247,12 +247,12 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb,
>  	pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid));
>  	if (!pctx) {
>  		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
> -		return -1;
> +		return 1;
>  	}
>  
>  	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
>  		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
> -		return -1;
> +		return 1;
>  	}
>  
>  	/* Get rid of the GTP + UDP headers. */
> -- 
> 2.10.2
>
Andreas Schultz Jan. 24, 2017, 8:02 p.m.
Hi Pablo,

----- On Jan 24, 2017, at 8:03 PM, pablo pablo@netfilter.org wrote:

> Hi Andreas,
> 
> On Tue, Jan 24, 2017 at 06:24:02PM +0100, Andreas Schultz wrote:
>> enable userspace to send error replies for invalid tunnels
>> 
>> Signed-off-by: Andreas Schultz <aschultz@tpip.net>
>> ---
>>  drivers/net/gtp.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
>> index 912721e..c607333 100644
>> --- a/drivers/net/gtp.c
>> +++ b/drivers/net/gtp.c
>> @@ -198,12 +198,12 @@ static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct
>> sk_buff *skb,
>>  	pctx = gtp0_pdp_find(gtp, be64_to_cpu(gtp0->tid));
>>  	if (!pctx) {
>>  		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
>> -		return -1;
>> +		return 1;
>>  	}
>>  
>>  	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
>>  		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
>> -		return -1;
>> +		return 1;
> 
> So userspace gets the packet that we cannot forward. I guess your
> userspace codebase performs this sanity checks again so you can send
> the appropriate error reply?

For TEID /= 0, the only reply is a T-PDU of type error indication. There
is no cause specified. So I don't actually have to repeat the check.
TEID == 0 is more interesting, this tells userspace that it tried to
send on an invalid tunnel and should tear it down.

If you like, you can have a look at the userspace code. The relevant piece
is at https://github.com/travelping/gtp_u_kmod/blob/master/src/gtp_u_kmod_port.erl#L231

But be warned, it's written in Erlang ;-)

Andreas

> 
>>  	}
>>  
>>  	/* Get rid of the GTP + UDP headers. */
>> @@ -247,12 +247,12 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp,
>> struct sk_buff *skb,
>>  	pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid));
>>  	if (!pctx) {
>>  		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
>> -		return -1;
>> +		return 1;
>>  	}
>>  
>>  	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
>>  		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
>> -		return -1;
>> +		return 1;
>>  	}
>>  
>>  	/* Get rid of the GTP + UDP headers. */
>> --
>> 2.10.2
Pablo Neira Jan. 24, 2017, 8:19 p.m.
On Tue, Jan 24, 2017 at 09:02:31PM +0100, Andreas Schultz wrote:
> Hi Pablo,
> 
> ----- On Jan 24, 2017, at 8:03 PM, pablo pablo@netfilter.org wrote:
> 
> > Hi Andreas,
> > 
> > On Tue, Jan 24, 2017 at 06:24:02PM +0100, Andreas Schultz wrote:
> >> enable userspace to send error replies for invalid tunnels
> >> 
> >> Signed-off-by: Andreas Schultz <aschultz@tpip.net>
> >> ---
> >>  drivers/net/gtp.c | 8 ++++----
> >>  1 file changed, 4 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
> >> index 912721e..c607333 100644
> >> --- a/drivers/net/gtp.c
> >> +++ b/drivers/net/gtp.c
> >> @@ -198,12 +198,12 @@ static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct
> >> sk_buff *skb,
> >>  	pctx = gtp0_pdp_find(gtp, be64_to_cpu(gtp0->tid));
> >>  	if (!pctx) {
> >>  		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
> >> -		return -1;
> >> +		return 1;
> >>  	}
> >>  
> >>  	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
> >>  		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
> >> -		return -1;
> >> +		return 1;
> > 
> > So userspace gets the packet that we cannot forward. I guess your
> > userspace codebase performs this sanity checks again so you can send
> > the appropriate error reply?
> 
> For TEID /= 0, the only reply is a T-PDU of type error indication. There
> is no cause specified. So I don't actually have to repeat the check.
> TEID == 0 is more interesting, this tells userspace that it tried to
> send on an invalid tunnel and should tear it down.

Ah, I see, thanks for explaining, I guess this is good to debug
misconfigurations.

> If you like, you can have a look at the userspace code. The relevant piece
> is at https://github.com/travelping/gtp_u_kmod/blob/master/src/gtp_u_kmod_port.erl#L231
> 
> But be warned, it's written in Erlang ;-)

Will have a look, but you taking me away from my usual domains :).

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diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 912721e..c607333 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -198,12 +198,12 @@  static int gtp0_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb,
 	pctx = gtp0_pdp_find(gtp, be64_to_cpu(gtp0->tid));
 	if (!pctx) {
 		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
-		return -1;
+		return 1;
 	}
 
 	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
 		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
-		return -1;
+		return 1;
 	}
 
 	/* Get rid of the GTP + UDP headers. */
@@ -247,12 +247,12 @@  static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb,
 	pctx = gtp1_pdp_find(gtp, ntohl(gtp1->tid));
 	if (!pctx) {
 		netdev_dbg(gtp->dev, "No PDP ctx to decap skb=%p\n", skb);
-		return -1;
+		return 1;
 	}
 
 	if (!gtp_check_src_ms(skb, pctx, hdrlen)) {
 		netdev_dbg(gtp->dev, "No PDP ctx for this MS\n");
-		return -1;
+		return 1;
 	}
 
 	/* Get rid of the GTP + UDP headers. */