Saint Dirty COW, Sacred Cow of the Race Condition

Patron of Linux kernels in every phone and server, copy-on-write, and race conditions won by a hair.

Life

On 20 October 2016 Phil Oester reported a race condition in the Linux kernel's copy-on-write mechanism: with the right timing an ordinary user could write to read-only memory pages and become root. The bug had lived in the kernel since 2007 and was everywhere, from servers to Android phones. It was so reliable that it was used in real attacks at once.

Prayer

O Saint Dirty COW, cow that writes where it is forbidden, let our read-only pages stay read-only. Amen.

How to celebrate

Celebrated by updating the kernel past 4.8.3 and admiring the cow sticker that many still remember.

A dirty cow writes where it must not.