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

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Message-ID: <CANaxB-wASWa1k6X5umJ=wt-K47uiBo9N5hxc--xz5cmU2bvysA@mail.gmail.com>
Date:   Tue, 24 Jan 2023 09:58:02 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        krisman@...labora.com, tglx@...utronix.de, luto@...nel.org,
        peterz@...radead.org, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, adobriyan@...il.com, corbet@....net,
        shuah@...nel.org
Subject: Re: [PATCH 3/3] ptrace,syscall_user_dispatch: add a getter/setter for
 sud configuration

On Tue, Jan 24, 2023 at 8:54 AM Gregory Price
<gregory.price@...verge.com> wrote:
>
> On Tue, Jan 24, 2023 at 05:43:47PM +0100, Oleg Nesterov wrote:
> > I won't really argue, but...
> >
> > On 01/24, Gregory Price wrote:
> > >
> > > 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.
> >
> > Rather than read /proc/pid/status, CRIU can just do
> > PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG unconditionally
> > and check syscall_user_dispatch_config.mode ?
> >
> > Why do want to expose SYSCALL_USER_DISPATCH in /proc/status? If this task
> > is not stopped you can't trust this value anyway. If it is stopped, I don't
> > think ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG) is slower than reading
> > /proc.
> >
> > but perhaps I missed something?
> >
> > Oleg.
> >
>
> *facepalm* good point, i'm wondering if there's a reason CRIU doesn't do
> the same for SECCOMP.

Because information about seccomp was in /proc/pid/status forever and we
started using it before the ptrace interface was merged. I am not sure that
this is the only reason, but  it is definitely one of them.

>
> either way, going to drop it