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Linux Virtual Ethernet Bug Delivers Corrupt TCP/IP Data (vijayp.ca)
jones_supa writes: Vijay Pandurangan from Twitter warns about a Linux kernel bug that causes containers using Virtual Ethernet devices for network routing to not check TCP checksums. Examples of software stacks that use Virtual Ethernet devices are Docker on IPv6, Kubernetes, Google Container Engine and Mesos. The kernel flaw results in applications incorrectly receiving corrupt data in a number of situations, such as with bad networking hardware. The bug dates back at least 3 years or more – it is present in kernels as far back as the Twitter engineering team has tested. Their patch has been reviewed and accepted into the kernel, and is currently being backported to -stable releases back to 3.14 in various distributions. If you use containers in your setup, Pandurangan recommends that you deploy a kernel with this patch.
Most NICs don't drop packets with bad L3/L4 checksums. Instead they flag them as bad and pass them to software, and the packet doesn't get checked until it hits the TCP/IP stack. The problem is that in this configuration, the packet arrives and the physical NIC and is flagged as bad, but when it is passed through the veth device that flag is intentionally cleared, and only after passing through the veth device does it hit the TCP/IP stack. Because the checksum was marked as good the stack trusts it and passes the data up to the socket.