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  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 22 May 2007 21:47:22 +0000
From:	"Thomas B. Rücker" <>
CC:	Philipp Gühring <>
Subject: UDP checksum broken since 2.6.18?


a friend of mine recently contacted me about what he at first thought
were IPv6 issues with some java software.

As it turns out it probably is a general IP issue with the Linux kernel:

He wrote this piece of c which sends an UDP packet to -
Packets generated by this code were captured by tcpdump and wireshark.
When feeding the dump into wireshark it says:
"Checksum: 0x62fd [incorrect, should be 0xe4f3]" for the udp packet.

We've tested this on several kernel versions.
Wireshark reports checksum broken:
Linux version 2.6.18-4-vserver-686 (Debian 2.6.18.dfsg.1-12)
( (gcc version 4.1.2 20061115 (prerelease) (Debian
4.1.1-21)) #1 SMP Mon Mar 26 19:55:22 UTC 2007
Linux version 2.6.19-dm8tbr-1 (root@...ron) (gcc version 4.1.2 20061028
(prerelease) (Debian 4.1.1-19)) #3 SMP PREEMPT Sun Dec 3 18:31:00 CET
2006 - (that's vanilla)
Linux version (root@...ron) (gcc version 4.1.2
20061115 (prerelease) (Debian 4.1.1-21)) #3 SMP Fri May 18 09:04:55 CEST
2007 - (that's vanilla + dscape patch)

Wireshark reports checksum ok:
Linux version (geeko@...ldhost) (gcc version 4.1.0
(SUSE Linux)) #1 Wed May 3 04:53:23 UTC 2006
Linux version 2.6.17-11-386 (root@...ranova) (gcc version 4.1.2 20060928
(prerelease) (Ubuntu 4.1.1-13ubuntu5)) #2 Tue Mar 13 23:30:30 UTC 2007
(Ubuntu 2.6.17-11.37-386)

So my guess is something between 2.6.17 and 2.6.18 broke.

Second option is: The way you are supposed to send UDP packets changed
in 2.6.18 and sun javavm and that piece of c are broken for the same reason.

Third option: everything is perfectly ok, the UDP checksum is computed
in a different way since 2.6.18 - due to some reason I don't know - and
Wireshark is broken.

We'd be grateful for some enlightment.



PS: please keep me CCed - I'm not subscribed to the netdev ml.

To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists