Re: [Bugme-new] [Bug 16216] New: wrong source addr of UDP packets when using policy routing

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 15 Jun 2010 15:14:43 GMT bugzilla-daemon@bugzilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=16216
> 
>            Summary: wrong source addr of UDP packets when using policy
>                     routing
>            Product: Networking
>            Version: 2.5
>     Kernel Version: 2.6.24.7

The reporter has confirmed that this issue persistes in 2.6.34.

>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV4
>         AssignedTo: shemminger@linux-foundation.org
>         ReportedBy: borg@uu3.net
>         Regression: No
> 
> 
> When policy routing is used, UDP packets have wrong source address.
> Source addr is probably taken from looking up routing table (main) to given
> destination instead of being set just after POSTROUTING, looking up cache.
> 
> This how it looks like doing simple netcat test:
> (tcpdump is run on aa.aa.47.90)
> 16:38:02.053053 IP aa.aa.47.67.32826 > aa.aa.47.90.660: UDP, length 8
> 16:38:05.660394 IP bb.bbb.241.62.660 > aa.aa.47.67.32826: UDP, length 8
> 
> aa.aa.47.90 have specific setup having 3 routing tables: main, 10, 20
> and all of them have default gateway. bb.bbb.241.62 is an addr of 
> outgoing interface of default route from main table.
> If a packet cames from specific interface
> its being stored to ipset and when packet is going to be sent out of the box
> its being marked in mangle OUTPUT matching specific ipset:
> 
> ### mangle PREROUTING ###
> fw="iptables -t mangle -A PREROUTING"
> $fw -i vlan0.13 -j SET --add-set gw10 src
> $fw -i lan2 -j SET --add-set gw20 src
> 
> ### mangle OUTPUT ###
> fw="iptables -t mangle -A OUTPUT"
> $fw -m set --set gw10 dst -j MARK --set-mark 10
> $fw -m set --set gw10 dst -j ACCEPT
> $fw -m set --set gw20 dst -j MARK --set-mark 20
> $fw -m set --set gw20 dst -j ACCEPT
> 
> % ip rule show
> 32764:  from all fwmark 0x14 lookup 20
> 32765:  from all fwmark 0xa lookup 10
> 
> Problem was noticed for UDP packets (openvpn connections are not working).
> Other non connection oriented protocols might be affected too.
> TCP (as connection oriented protocol) works just fine.
>