Re: [PATCH] prctl: add PR_[GS]ET_KILLABLE

On Tue, 2018-07-31 at 18:26 +0200, Jann Horn wrote:

On Mon, Jul 30, 2018 at 10:01 AM Jürg Billeter [off-list ref] wrote:

[...]

quoted

diff --git a/kernel/sys.c b/kernel/sys.c
index 38509dc1f77b..264de630d548 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c

[...]

quoted

+       case PR_SET_KILLABLE:
+               if (arg2 != 1 || arg3 || arg4 || arg5)
+                       return -EINVAL;
+               me->signal->flags &= ~SIGNAL_UNKILLABLE;
+               break;

I don't have an opinion on this patchset otherwise, but should this
prctl maybe block PR_SET_KILLABLE if you're actually the real init
process? This seems like it could potentially lead to weird things.

While I don't expect global init to use this, I can't think of a good
reason to disallow it in the kernel. Do you have specific concerns or
is the code in kernel/fork.c the only reason? I prefer avoiding special
cases unless really required.

This code in kernel/fork.c seems to rely on the fact that global init
is SIGNAL_UNKILLABLE, and probably also leads to weirdness if
container init is non-SIGNAL_UNKILLABLE:

Yes, Oleg has mentioned this as well. I have to change copy_process()
to directly check for the PID namespace root process instead of
checking for SIGNAL_UNKILLABLE.

Jürg