netdev - Re: traceroute failure in kernel 6.1 and 6.2

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Message-ID: <CANn89iK1aPiystTAk2qTnzsN-LFskJ4BxL=XgTk2aLpExrWFEw@mail.gmail.com>
Date:   Mon, 23 Jan 2023 16:21:08 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mantas Mikulėnas <grawity@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: traceroute failure in kernel 6.1 and 6.2

On Sat, Jan 21, 2023 at 7:09 PM Mantas Mikulėnas <grawity@...il.com> wrote:
>
> Hello,
>
> Not sure whether this has been reported, but:
>
> After upgrading from kernel 6.0.7 to 6.1.6 on Arch Linux, unprivileged
> ICMP traceroute using the `traceroute -I` tool stopped working – it very
> reliably fails with a "No route to host" at some point:
>
>         myth> traceroute -I 83.171.33.188
>         traceroute to 83.171.33.188 (83.171.33.188), 30 hops max, 60
>         byte packets
>          1  _gateway (192.168.1.1)  0.819 ms
>         send: No route to host
>         [exited with 1]
>
> while it still works for root:
>
>         myth> sudo traceroute -I 83.171.33.188
>         traceroute to 83.171.33.188 (83.171.33.188), 30 hops max, 60
>         byte packets
>          1  _gateway (192.168.1.1)  0.771 ms
>          2  * * *
>          3  10.69.21.145 (10.69.21.145)  47.194 ms
>          4  82-135-179-168.static.zebra.lt (82.135.179.168)  49.124 ms
>          5  213-190-41-3.static.telecom.lt (213.190.41.3)  44.211 ms
>          6  193.219.153.25 (193.219.153.25)  77.171 ms
>          7  83.171.33.188 (83.171.33.188)  78.198 ms
>
> According to `git bisect`, this started with:
>
>         commit 0d24148bd276ead5708ef56a4725580555bb48a3
>         Author: Eric Dumazet <edumazet@...gle.com>
>         Date:   Tue Oct 11 14:27:29 2022 -0700
>
>             inet: ping: fix recent breakage
>
>
>
>
> It still happens with a fresh 6.2rc build, unless I revert that commit.
>
> The /bin/traceroute is the one that calls itself "Modern traceroute for
> Linux, version 2.1.1", on Arch Linux. It seems to use socket(AF_INET,
> SOCK_DGRAM, IPPROTO_ICMP), has neither setuid nor file capabilities.
> (The problem does not occur if I run it as root.)
>
> This version of `traceroute` sends multiple probes at once (with TTLs
> 1..16); according to strace, the first approx. 8-12 probes are sent
> successfully, but eventually sendto() fails with EHOSTUNREACH. (Though
> if I run it on local tty as opposed to SSH, it fails earlier.) If I use
> -N1 to have it only send one probe at a time, the problem doesn't seem
> to occur.



I was not able to reproduce the issue (downloading
https://sourceforge.net/projects/traceroute/files/latest/download)

I suspect some kind of bug in this traceroute, when/if some ICMP error
comes back.

Double check by

tcpdump -i ethXXXX icmp

While you run traceroute -I ....