Re: [PATCH] proc: allow killing processes via file descriptors

On Sun, Nov 18, 2018 at 4:53 PM, Daniel Colascione [off-list ref] wrote:

quoted

Sure, I'd propose that ptrace_may_access() is what we should use for
operation permission checks.

The tricky part is that ptrace_may_access takes a struct task. We want
logic that's *like* ptrace_may_access, but that works posthumously.
It's especially tricky because there's an LSM hook that lets
__ptrace_may_access do arbitrary things. And we can't just run that
hook upon process death, since *after* a process dies, a process
holding an exithand FD (or whatever we call it) may pass that FD to
another process, and *that* process can read(2) from it.

Another option is doing the exithand access check at open time. I
think that's probably fine, and it would make things a lot simpler.
But if we use this option, we should understand what we're doing, and
get some security-conscious people to think through the implications.

A ptrace check is also probably too strict. Yama's ptrace_scope
feature will block ptrace between unrelated processes within a single
user context, but applying this restriction to exit code monitoring
seems too severe to me.