netdev - Re: [PATCH net v3] selftests/fib_tests: Rework fib_rp_filter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20211201193527.GA27000@bytedance>
Date:   Wed, 1 Dec 2021 11:35:27 -0800
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Peilin Ye <peilin.ye@...edance.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v3] selftests/fib_tests: Rework fib_rp_filter_test()

Hi David,

On Wed, Dec 01, 2021 at 11:00:26AM -0700, David Ahern wrote:
> On 11/30/21 5:47 PM, Peilin Ye wrote:
> >  ┌─────────────────────────────┐    ┌─────────────────────────────┐
> >  │  network namespace 1 (ns1)  │    │  network namespace 2 (ns2)  │
> >  │                             │    │                             │
> >  │  ┌────┐     ┌─────┐         │    │  ┌─────┐            ┌────┐  │
> >  │  │ lo │<───>│veth1│<────────┼────┼─>│veth2│<──────────>│ lo │  │
> >  │  └────┘     ├─────┴──────┐  │    │  ├─────┴──────┐     └────┘  │
> >  │             │192.0.2.1/24│  │    │  │192.0.2.1/24│             │
> >  │             └────────────┘  │    │  └────────────┘             │
> >  └─────────────────────────────┘    └─────────────────────────────┘
> 
> if the intention of the tests is to validate that rp_filter = 1 works as
> designed, then I suggest a simpler test. 2 namespaces, 2 veth pairs.
> Request goes through one interface, and the response comes in the other
> via routing in ns2. ns1 would see the response coming in the 'wrong'
> interface and drops it.

Quite the opposite - the goal is to make sure that commit 66f8209547cc
("fib: relax source validation check for loopback packets") _prevents_
packets from being dropped when rp_filter = 1 in this corner case, as I
mentioned in the commit message.

In order to test this corner case, I need a packet that:

  1. was received on lo;
  2. has a local source IP address (other than lo's 127.0.0.1/8, which
     is 192.0.2.1 in this case);
  3. has no dst attached to it (in this case since it was redirected
     from veth).

See __fib_validate_source():

+       dev_match = dev_match || (res.type == RTN_LOCAL &&
+                                 dev == net->loopback_dev);
					      ^^^^^^^^^^^^
This relaxed check only applies to lo, and I do need to redirect packets
from veth ingress to lo ingress in order to trigger this.

Thanks,
Peilin Ye