Re: [PATCH 3/3] ptrace,syscall_user_dispatch: add a getter/setter for sud configuration

[Gregory Price]

On Mon, Jan 23, 2023 at 08:52:29PM +0100, Oleg Nesterov wrote:
> On 01/23, Gregory Price wrote:
> >
> > So i think dropping 2/3 in the list is good.  If you concur i'll do
> > that.
> 
> Well I obviously think that 2/3 should be dropped ;)
> 
> As for 1/3 and 3/3, feel free to add my reviewed-by.
> 
> Oleg.
>

I'm actually going to walk my agreement back.

After one more review, the need for the proc/status entry is not to
decide whether to dump SUD settings, but for use in deciding whether to
set the SUSPEND_SYSCALL_DISPATCH option from patch 1/3.

For SECCOMP, CRIU's `compel` does the following:

1. ptrace attach / halt
2. examine proc/status for seccomp usage
3. if seccomp in use, set PTRACE_O_SUSPEND_SECCOMP
4. proceed with further operations

The same pattern would be used for syscall dispatch.

Technically I think setting the flag unconditionally would be safe, but
it would lead to unclear system state (i.e. did i actually suspend
something? was the process actually using it?)

To me it seems better to leave it explicit and keep the second commit.

Thoughts?

(cc: @avagin if you happen to have any input on this particular pattern)

~Gregory