linux-kernel - Re: [PATCH] seccomp: Add SECCOMP_CLONE

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Message-ID: <CAADnVQJSgcAjEnU-A9bF6-9MQRFvbHqRsCCY7a0Y6bhVGtcGpA@mail.gmail.com>
Date: Wed, 3 Sep 2025 15:44:47 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tom Hromatka <tom.hromatka@...cle.com>
Cc: Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>, Will Drewry <wad@...omium.org>, 
	Sargun Dhillon <sargun@...gun.me>, Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] seccomp: Add SECCOMP_CLONE_FILTER operation

On Wed, Sep 3, 2025 at 1:52 PM Tom Hromatka <tom.hromatka@...cle.com> wrote:
>
> On 9/3/25 2:45 PM, Alexei Starovoitov wrote:
> > On Wed, Sep 3, 2025 at 1:38 PM Tom Hromatka <tom.hromatka@...cle.com> wrote:
> >>
> >> +
> >> +       spin_lock_irq(&current->sighand->siglock);
> >> +       spin_lock_irq(&task->sighand->siglock);
> >> +
> >> +       if (atomic_read(&task->seccomp.filter_count) == 0) {
> >> +               spin_unlock_irq(&task->sighand->siglock);
> >> +               spin_unlock_irq(&current->sighand->siglock);
> >
> > did you copy this pattern from somewhere ?
> > It's obviously buggy.
>
> I tried to mimic the logic in copy_seccomp() in kernel/fork.c,
> but as you point out, I probably messed it up :).
>
> Do you have recommendations for a better design pattern?

Several things look wrong here.
Double _irq() is one obvious bug.
Grabbing spin_lock to do atomic_read() is another oddity.