Linux: buffer overrun in netback due to unusual packet

ISSUE DESCRIPTION

The fix for XSA-423 added logic to Linux’es netback driver to deal with a frontend splitting a packet in a way such that not all of the headers would come in one piece. Unfortunately the logic introduced there didn’t account for the extreme case of the entire packet being split into as many pieces as permitted by the protocol, yet still being smaller than the area that’s specially dealt with to keep all (possible) headers together. Such an unusual packet would therefore trigger a buffer overrun in the driver.

IMPACT

An unprivileged guest can cause Denial of Service (DoS) of the host by sending network packets to the backend, causing the backend to crash.
Data corruption or privilege escalation seem unlikely but have not been ruled out.

VULNERABLE SYSTEMS

All systems using a Linux based network backend with kernel 3.19 and newer are vulnerable, on the assumption that the fix for XSA-423 was taken. Systems using other network backends are not known to be vulnerable.