Re: Pasta 20240726 and newer crash with ASSERTION FAILED in flow_hash

[Stefano Brivio <sbrivio@redhat.com>]

Hi Matt,

On Tue, 13 Aug 2024 22:58:42 -0700
Matt Hamilton <matt@thmail.io> wrote:

> I am using Podman in Fedora 40, which uses pasta by default for rootless 
> container networking.
> 
> Fedora 40's base version of passt is `passt-0^20240326.g4988e2b-1.fc40`, 
> but recently two newer versions were released, 
> `passt-0^20240726.g57a21d2-1.fc40` and `0^20240806.gee36266-1.fc40`.
> 
> After upgrading, one pod kept going offline after a few minutes. The 
> containers remained running, but could not make outbound connections. 
> Journalctl revealed that the pasta process for the pod had crashed with:
> 
>     Aug 08 23:07:55 dev pasta[95859]: ASSERTION FAILED in flow_hash
>     (flow.c:566): pif != PIF_NONE && !inany_is_unspecified(&side->eaddr)
>     && side->eport != 0 && side->fport != 0
>     Aug 08 23:07:55 dev audit[95859]: SECCOMP auid=1000 uid=1000
>     gid=1000 ses=1
>     subj=unconfined_u:unconfined_r:container_runtime_t:s0-s0:c0.c1023
>     pid=95859 comm="pasta.avx2" exe="/usr/bin/pasta.avx2" sig=31
>     arch=c000003e syscall=186 compat=0 ip=0x7f8f8c23b64f code=0x80000000
>     Aug 08 23:07:55 dev audit[95859]: ANOM_ABEND auid=1000 uid=1000
>     gid=1000 ses=1
>     subj=unconfined_u:unconfined_r:container_runtime_t:s0-s0:c0.c1023
>     pid=95859 comm="pasta.avx2" exe="/usr/bin/pasta.avx2" sig=31 res=1
> 
> After much debugging, I isolated the trigger to a particular container 
> making a peer-to-peer TCP connection to a remote address with port 0.

Thanks for the analysis and for the report!

> Reverting passt to version 20240326 works as expected, and the container 
> stays online. It's been a long time since I wrote any C, but the code 
> seems clear and checks that the endpoint and forwarding ports do not 
> equal 0. I assume that a port 0 connection is not realistic or useful,  
> and that actual attempt to connect over this port indicate a bug in the 
> client code. Is this correct?

Right, that's somehow unexpected because TCP port zero is reserved
and not assigned, so it should never be used. However, I'm not sure how
we can even reach flow_hash() with it.

David, this seems to come from 163a339214dd ("tcp, flow: Replace TCP
specific hash function with general flow hash"), any clue?

-- 
Stefano