Subject: Re: [PATCH v4 net-next] net: multipath routing: configurable seed

From: Pavel Balaev <[email-masked]>
Date: Tue, 27 Apr 2021 12:42:20 +0300

On Mon, Apr 26, 2021 at 09:21:53PM -0600, David Ahern wrote:
> On 4/23/21 6:44 AM, Balaev Pavel wrote:
> > Ability for a user to assign seed value to multipath route hashes.
> > Now kernel uses random seed value to prevent hash-flooding DoS attacks;
> > however, it disables some use cases, f.e:
> > 
> > +-------+        +------+        +--------+
> > |       |-eth0---| FW0  |---eth0-|        |
> > |       |        +------+        |        |
> > |  GW0  |ECMP                ECMP|  GW1   |
> > |       |        +------+        |        |
> > |       |-eth1---| FW1  |---eth1-|        |
> > +-------+        +------+        +--------+
> > 
> > In this use case, two ECMP routers balance traffic between two firewalls.
> > If some flow transmits a response over a different channel than request,
> > such flow will be dropped, because keep-state rules are created on
> > the other firewall.
> > 
> > This patch adds sysctl variable: net.ipv4|ipv6.fib_multipath_hash_seed.
> > User can set the same seed value on GW0 and GW1 for traffic to be
> > mirror-balanced. By default, random value is used.
> > 
> > Signed-off-by: Balaev Pavel <[email-masked]>
> > ---
> >  Documentation/networking/ip-sysctl.rst        |  14 +
> >  include/net/flow_dissector.h                  |   4 +
> >  include/net/netns/ipv4.h                      |   2 +
> >  include/net/netns/ipv6.h                      |   3 +
> >  net/core/flow_dissector.c                     |   9 +
> >  net/ipv4/route.c                              |  10 +-
> >  net/ipv4/sysctl_net_ipv4.c                    |  97 +++++
> >  net/ipv6/route.c                              |  10 +-
> >  net/ipv6/sysctl_net_ipv6.c                    |  96 +++++
> >  .../testing/selftests/net/forwarding/Makefile |   1 +
> >  tools/testing/selftests/net/forwarding/lib.sh |  41 +++
> >  .../net/forwarding/router_mpath_seed.sh       | 347 ++++++++++++++++++
> >  12 files changed, 632 insertions(+), 2 deletions(-)
> >  create mode 100755 tools/testing/selftests/net/forwarding/router_mpath_seed.sh
> 
> this really needs to be multiple patches. At a minimum 1 for ipv4, 1 for
> ipv6 and 1 for the test script (thank you for adding that).
> 
> [ cc'ed Ido since most of the tests under
> tools/testing/selftests/net/forwarding come from him and team ]

OK, I will create 3 patches. Thanks for the advice.

> > 
> > diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> > index 9701906f6..d1a67e6fe 100644
> > --- a/Documentation/networking/ip-sysctl.rst
> > +++ b/Documentation/networking/ip-sysctl.rst
> > @@ -100,6 +100,20 @@ fib_multipath_hash_policy - INTEGER
> >  	- 1 - Layer 4
> >  	- 2 - Layer 3 or inner Layer 3 if present
> >  
> > +fib_multipath_hash_seed - STRING
> > +	Controls seed value for multipath route hashes. By default
> > +	random value is used. Only valid for kernels built with
> > +	CONFIG_IP_ROUTE_MULTIPATH enabled.
> > +
> > +	Valid format: two hex values set off with comma or "random"
> > +	keyword.
> > +
> > +	Example to generate the seed value::
> > +
> > +		RAND=$(openssl rand -hex 16) && echo "${RAND:0:16},${RAND:16:16}"
> > +
> > +	Default: "random"
> > +
> >  fib_sync_mem - UNSIGNED INTEGER
> >  	Amount of dirty memory from fib entries that can be backlogged before
> >  	synchronize_rcu is forced.
> > diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
> > index ffd386ea0..2bd4e28de 100644
> > --- a/include/net/flow_dissector.h
> > +++ b/include/net/flow_dissector.h
> > @@ -348,6 +348,10 @@ static inline bool flow_keys_have_l4(const struct flow_keys *keys)
> >  }
> >  
> >  u32 flow_hash_from_keys(struct flow_keys *keys);
> > +#ifdef CONFIG_IP_ROUTE_MULTIPATH
> > +u32 flow_multipath_hash_from_keys(struct flow_keys *keys,
> > +			   const siphash_key_t *seed);
> 
> column alignment looks off here ^^^^ and a few other places; please
> correct in the next version.
> 
After running "scripts/checkpatch.pl" I got warnings about alignment.
So I run checkpatch.pl --fix and fixed alignment as a script did.
So warnings goes away. I don't get the rules of alignment, can you 
tell me the right way?