[PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Santucci Pierpaolo]

From second fragment on, IPV6FR program must stop the dissection of IPV6
fragmented packet. This is the same approach used for IPV4 fragmentation.

Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
---
 tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
index 5a65f6b51377..95a5a0778ed7 100644
--- a/tools/testing/selftests/bpf/progs/bpf_flow.c
+++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
@@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
 		 */
 		if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
 			return export_flow_keys(keys, BPF_OK);
+	} else {
+		return export_flow_keys(keys, BPF_OK);
 	}
 
 	return parse_ipv6_proto(skb, fragh->nexthdr);
-- 
2.29.2

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Andrii Nakryiko]

On Tue, Nov 10, 2020 at 9:12 AM Santucci Pierpaolo
<santucci@epigenesys.com> wrote:
>
> From second fragment on, IPV6FR program must stop the dissection of IPV6
> fragmented packet. This is the same approach used for IPV4 fragmentation.
>

Jakub, can you please take a look as well?

> Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
> ---
>  tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
> index 5a65f6b51377..95a5a0778ed7 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_flow.c
> +++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
> @@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
>                  */
>                 if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
>                         return export_flow_keys(keys, BPF_OK);
> +       } else {
> +               return export_flow_keys(keys, BPF_OK);
>         }
>
>         return parse_ipv6_proto(skb, fragh->nexthdr);
> --
> 2.29.2
>

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Jakub Sitnicki]

On Wed, Nov 11, 2020 at 05:48 AM CET, Andrii Nakryiko wrote:
> On Tue, Nov 10, 2020 at 9:12 AM Santucci Pierpaolo
> <santucci@epigenesys.com> wrote:
>>
>> From second fragment on, IPV6FR program must stop the dissection of IPV6
>> fragmented packet. This is the same approach used for IPV4 fragmentation.
>>
>
> Jakub, can you please take a look as well?

I'm not initimately familiar with this test, but looking at the change
I'd consider that Destinations Options and encapsulation headers can
follow the Fragment Header.

With enough of Dst Opts or levels of encapsulation, transport header
could be pushed to the 2nd fragment. So I'm not sure if the assertion
from the IPv4 dissector that 2nd fragment and following doesn't contain
any parseable header holds.

Taking a step back... what problem are we fixing here?

>
>> Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
>> ---
>>  tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
>> index 5a65f6b51377..95a5a0778ed7 100644
>> --- a/tools/testing/selftests/bpf/progs/bpf_flow.c
>> +++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
>> @@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
>>                  */
>>                 if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
>>                         return export_flow_keys(keys, BPF_OK);
>> +       } else {
>> +               return export_flow_keys(keys, BPF_OK);
>>         }
>>
>>         return parse_ipv6_proto(skb, fragh->nexthdr);
>> --
>> 2.29.2
>>

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Santucci Pierpaolo]

Hi Jakub,

thanks for your reply.

Let me explain the problem with an example.

Please consider the PCAP file:
https://github.com/named-data/ndn-tools/blob/master/tests/dissect-wireshark/ipv6-udp-fragmented.pcap
Let's assume that the dissector is invoked without the flag:
BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL.
 
Without the proposed patch, the flow keys for the second fragment (packet
timestamp 0.256997) will contain the value 0x6868 for the source and
destination port fields: this is obviously wrong.
The same happens for the third fragment (packet timestamp 0.256998) and for
the fourth fragment (packet timestamp 0.257001).

So it seems that the correct thing to do is to stop the dissector after the
IPV6 fragmentation header for all fragments from the second on.

Regards,
    Pierpaolo Santucci

On Wed, Nov 11, 2020 at 12:17:06PM +0100, Jakub Sitnicki wrote:
> On Wed, Nov 11, 2020 at 05:48 AM CET, Andrii Nakryiko wrote:
> > On Tue, Nov 10, 2020 at 9:12 AM Santucci Pierpaolo
> > <santucci@epigenesys.com> wrote:
> >>
> >> From second fragment on, IPV6FR program must stop the dissection of IPV6
> >> fragmented packet. This is the same approach used for IPV4 fragmentation.
> >>
> >
> > Jakub, can you please take a look as well?
> 
> I'm not initimately familiar with this test, but looking at the change
> I'd consider that Destinations Options and encapsulation headers can
> follow the Fragment Header.
> 
> With enough of Dst Opts or levels of encapsulation, transport header
> could be pushed to the 2nd fragment. So I'm not sure if the assertion
> from the IPv4 dissector that 2nd fragment and following doesn't contain
> any parseable header holds.
> 
> Taking a step back... what problem are we fixing here?
> 
> >
> >> Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
> >> ---
> >>  tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
> >> index 5a65f6b51377..95a5a0778ed7 100644
> >> --- a/tools/testing/selftests/bpf/progs/bpf_flow.c
> >> +++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
> >> @@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
> >>                  */
> >>                 if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
> >>                         return export_flow_keys(keys, BPF_OK);
> >> +       } else {
> >> +               return export_flow_keys(keys, BPF_OK);
> >>         }
> >>
> >>         return parse_ipv6_proto(skb, fragh->nexthdr);
> >> --
> >> 2.29.2
> >>

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Daniel Borkmann]

On 11/11/20 3:12 PM, Santucci Pierpaolo wrote:
> Hi Jakub,
> 
> thanks for your reply.

(Santucci, please do not top-post but always reply inline which makes it
  easier for discussions to follow.)

> Let me explain the problem with an example.
> 
> Please consider the PCAP file:
> https://github.com/named-data/ndn-tools/blob/master/tests/dissect-wireshark/ipv6-udp-fragmented.pcap
> Let's assume that the dissector is invoked without the flag:
> BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL.
>   
> Without the proposed patch, the flow keys for the second fragment (packet
> timestamp 0.256997) will contain the value 0x6868 for the source and
> destination port fields: this is obviously wrong.
> The same happens for the third fragment (packet timestamp 0.256998) and for
> the fourth fragment (packet timestamp 0.257001).
> 
> So it seems that the correct thing to do is to stop the dissector after the
> IPV6 fragmentation header for all fragments from the second on.
> 
[...]
>>
>> I'm not initimately familiar with this test, but looking at the change
>> I'd consider that Destinations Options and encapsulation headers can
>> follow the Fragment Header.
>>
>> With enough of Dst Opts or levels of encapsulation, transport header
>> could be pushed to the 2nd fragment. So I'm not sure if the assertion
>> from the IPv4 dissector that 2nd fragment and following doesn't contain
>> any parseable header holds.

Hm, staring at rfc8200, it says that the first fragment packet must include
the upper-layer header (e.g. tcp, udp). The patch here should probably add a
comment wrt to the rfc.

Thanks,
Daniel

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[Jakub Sitnicki]

On Thu, Nov 12, 2020 at 12:06 AM CET, Daniel Borkmann wrote:

[...]

>>> I'm not initimately familiar with this test, but looking at the change
>>> I'd consider that Destinations Options and encapsulation headers can
>>> follow the Fragment Header.
>>>
>>> With enough of Dst Opts or levels of encapsulation, transport header
>>> could be pushed to the 2nd fragment. So I'm not sure if the assertion
>>> from the IPv4 dissector that 2nd fragment and following doesn't contain
>>> any parseable header holds.
>
> Hm, staring at rfc8200, it says that the first fragment packet must include
> the upper-layer header (e.g. tcp, udp). The patch here should probably add a
> comment wrt to the rfc.

You're right, it clearly says so. Nevermind my worries about malformed
packets then. Change LGTM:

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

Re: [PATCH] selftest/bpf: fix IPV6FR handling in flow dissector

[John Fastabend]

Jakub Sitnicki wrote:
> On Thu, Nov 12, 2020 at 12:06 AM CET, Daniel Borkmann wrote:
> 
> [...]
> 
> >>> I'm not initimately familiar with this test, but looking at the change
> >>> I'd consider that Destinations Options and encapsulation headers can
> >>> follow the Fragment Header.
> >>>
> >>> With enough of Dst Opts or levels of encapsulation, transport header
> >>> could be pushed to the 2nd fragment. So I'm not sure if the assertion
> >>> from the IPv4 dissector that 2nd fragment and following doesn't contain
> >>> any parseable header holds.
> >
> > Hm, staring at rfc8200, it says that the first fragment packet must include
> > the upper-layer header (e.g. tcp, udp). The patch here should probably add a
> > comment wrt to the rfc.
> 
> You're right, it clearly says so. Nevermind my worries about malformed
> packets then. Change LGTM:
> 
> Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

Also please add some of the details discussed here to the commit msg so
we can remember this next time. 

Thanks!

[PATCH v2] selftest/bpf: fix IPV6FR handling in flow dissector

[Santucci Pierpaolo]

From second fragment on, IPV6FR program must stop the dissection of IPV6
fragmented packet. This is the same approach used for IPV4 fragmentation.
This fixes the flow keys calculation for the upper-layer protocols.
Note that according to RFC8200, the first fragment packet must include
the upper-layer header.

Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
---
v2: extend the commit message, as suggested by John Fastabend
    <john.fastabend@gmail.com>

 tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
index 5a65f6b51377..95a5a0778ed7 100644
--- a/tools/testing/selftests/bpf/progs/bpf_flow.c
+++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
@@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
 		 */
 		if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
 			return export_flow_keys(keys, BPF_OK);
+	} else {
+		return export_flow_keys(keys, BPF_OK);
 	}
 
 	return parse_ipv6_proto(skb, fragh->nexthdr);
-- 
2.17.5

Re: [PATCH v2] selftest/bpf: fix IPV6FR handling in flow dissector

[Jakub Sitnicki]

On Mon, Nov 16, 2020 at 11:30 AM CET, Santucci Pierpaolo wrote:
> From second fragment on, IPV6FR program must stop the dissection of IPV6
> fragmented packet. This is the same approach used for IPV4 fragmentation.
> This fixes the flow keys calculation for the upper-layer protocols.
> Note that according to RFC8200, the first fragment packet must include
> the upper-layer header.
>
> Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
> ---
> v2: extend the commit message, as suggested by John Fastabend
>     <john.fastabend@gmail.com>
>
>  tools/testing/selftests/bpf/progs/bpf_flow.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
> index 5a65f6b51377..95a5a0778ed7 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_flow.c
> +++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
> @@ -368,6 +368,8 @@ PROG(IPV6FR)(struct __sk_buff *skb)
>  		 */
>  		if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
>  			return export_flow_keys(keys, BPF_OK);
> +	} else {
> +		return export_flow_keys(keys, BPF_OK);
>  	}
>  
>  	return parse_ipv6_proto(skb, fragh->nexthdr);

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

Re: [PATCH v2] selftest/bpf: fix IPV6FR handling in flow dissector

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (refs/heads/master):

On Mon, 16 Nov 2020 11:30:37 +0100 you wrote:
> >From second fragment on, IPV6FR program must stop the dissection of IPV6
> fragmented packet. This is the same approach used for IPV4 fragmentation.
> This fixes the flow keys calculation for the upper-layer protocols.
> Note that according to RFC8200, the first fragment packet must include
> the upper-layer header.
> 
> Signed-off-by: Santucci Pierpaolo <santucci@epigenesys.com>
> 
> [...]

Here is the summary with links:
  - [v2] selftest/bpf: fix IPV6FR handling in flow dissector
    https://git.kernel.org/bpf/bpf-next/c/024cd2cbd1ca

You are awesome, thank you!
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