runc container escape via "masked path" abuse due to mount race conditions

runc is a CLI tool for spawning and running containers according to the OCIspecification. In versions 1.2.7 and below, 1.3.0-rc.1 through 1.3.1,1.4.0-rc.1 and 1.4.0-rc.2 files, runc would not perform sufficientverification that the source of the bind-mount (i.e., the container's/dev/null) was actually a real /dev/null inode when using the container's/dev/null to mask. This exposes two methods of attack: an arbitrary mountgadget, leading to host information disclosure, host denial of service,container escape, or a bypassing of maskedPaths. This issue is fixed inversions 1.2.8, 1.3.3 and 1.4.0-rc.3.

Where it's fixed