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([2601:282:800:fd80:5059:73bc:5255:ccf5]) by smtp.googlemail.com with ESMTPSA id j23sm19583011ioo.6.2019.07.17.14.59.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Jul 2019 14:59:20 -0700 (PDT) Subject: Re: [Patch net v3 1/2] fib: relax source validation check for loopback packets To: Cong Wang , netdev@vger.kernel.org Cc: Julian Anastasov References: <20190717214159.25959-1-xiyou.wangcong@gmail.com> <20190717214159.25959-2-xiyou.wangcong@gmail.com> From: David Ahern Message-ID: <4b5beb7c-a6f7-3a5e-d530-88638dde1ef9@gmail.com> Date: Wed, 17 Jul 2019 15:59:20 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190717214159.25959-2-xiyou.wangcong@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 7/17/19 3:41 PM, Cong Wang wrote: > In a rare case where we redirect local packets from veth to lo, > these packets fail to pass the source validation when rp_filter > is turned on, as the tracing shows: > > <...>-311708 [040] ..s1 7951180.957825: fib_table_lookup: table 254 oif 0 iif 1 src 10.53.180.130 dst 10.53.180.130 tos 0 scope 0 flags 0 > <...>-311708 [040] ..s1 7951180.957826: fib_table_lookup_nh: nexthop dev eth0 oif 4 src 10.53.180.130 > > So, the fib table lookup returns eth0 as the nexthop even though > the packets are local and should be routed to loopback nonetheless, > but they can't pass the dev match check in fib_info_nh_uses_dev() > without this patch. > > It should be safe to relax this check for this special case, as > normally packets coming out of loopback device still have skb_dst > so they won't even hit this slow path. > > Cc: Julian Anastasov > Cc: David Ahern > Signed-off-by: Cong Wang > --- > net/ipv4/fib_frontend.c | 5 +++++ > 1 file changed, 5 insertions(+) > Seems ok to me. Reviewed-by: David Ahern