Implement mount-cgroup in Golang style

[kmahyyg]

feat(exp/mount_cgroup.go): completely fix #35 in golang-style

This implemented mount-cgroup exploit totally in Golang.

Detailed information:

• Change whole "create-mount-write" process using Golang native Unix API.
• To avoid conflict, increase length of random string from 3 to 4.
  Tasks sub-cgroup are also in the same kind of random name.
• Read mounted filesystem information from /proc/self/mountinfo, instead of /etc/mtab .
• Due to the limitation of exec.Command, output redirect is implemented in another way: manually get pid and write to cgroups.procs

Further enhancement:

• To read the container filesystem path on the host, implement to read superBlockOptions of MountInfo.
• To implement CVE-2022-0492 in this PR further, I modified EscapeCgroup function, so that it can be re-used for other subsystems.

Chores:

• go mod tidy
• Fix Typo
• Run a much quicker random string generator

1b94046 (HEAD -> main, origin/main, origin/HEAD) feat(exp/mount_cgroup.go): completely fix #35 in golang-style
043d6b6 feat(util/cgroup.go): add superBlockOptions when parsing /proc/self/mountinfo
4c640ae fix(util/cgroup.go): typo: marjor -> major
60b44e5 fix(exp/mount-cgroup): fix #35 in shell-style in a simple way
ecfadba optimize(exp/mount-cgroup): update build constraint, cgroup is linux only
ef056df optimize(util/common.go): Quicker Random String Generator

[kmahyyg]

[neargle]

Awesome! Elegant implementation ~ more elegant than half of the code I wrote in TODO.

[neargle]

LGTM~

[neargle]

why sleep here？

[kmahyyg]

Well it need some time to read the PID of spawned /bin/sh, And also use /bin/sh -c echo $$ then put the command stdout to cgroup.procs will cause unknown reason error with exit code 1. So I use another way to achieve this.

You could also monitor this behaviour by adding auditd rule -a always,exit -F arch=b64 -S execve -F key=procmon which made debug much more easier than before.