landlock: Add ptrace restrictions

mainline inclusion
from mainline-v5.13-rc1
commit afe81f75
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6DJU0
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=afe81f754117dd96853677c5cb815f49abef0ba0



--------------------------------

Using ptrace(2) and related debug features on a target process can lead
to a privilege escalation.  Indeed, ptrace(2) can be used by an attacker
to impersonate another task and to remain undetected while performing
malicious activities.  Thanks to  ptrace_may_access(), various part of
the kernel can check if a tracer is more privileged than a tracee.

A landlocked process has fewer privileges than a non-landlocked process
and must then be subject to additional restrictions when manipulating
processes. To be allowed to use ptrace(2) and related syscalls on a
target process, a landlocked process must have a subset of the target
process's rules (i.e. the tracee must be in a sub-domain of the tracer).

Cc: James Morris <jmorris@namei.org>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: Jann Horn <jannh@google.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210422154123.13086-5-mic@digikod.net


Signed-off-by: James Morris <jamorris@linux.microsoft.com>
Signed-off-by: Yi Yang <yiyang13@huawei.com>