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

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Message-ID: <CAA-VZP=ZDsEESH0XJLiOp0CEBVR7DQn+dC82PdWzLqVTgSB_HA@mail.gmail.com>
Date: Fri, 5 Sep 2025 14:03:42 -0700
From: YiFei Zhu <zhuyifei@...gle.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Tom Hromatka <tom.hromatka@...cle.com>, kees@...nel.org, luto@...capital.net, 
	wad@...omium.org, sargun@...gun.me, corbet@....net, shuah@...nel.org, 
	brauner@...nel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] seccomp: Add SECCOMP_CLONE_FILTER operation

On Thu, Sep 4, 2025 at 10:51 AM Al Viro <viro@...iv.linux.org.uk> wrote:
> Looks like the only lockless reader is
>         struct seccomp_filter *f =
>                         READ_ONCE(current->seccomp.filter);
> in seccomp_run_filters(), so unless I've missed something (and "filter"
> is not a search-friendly name ;-/) we should be fine; that READ_ONCE()
> is there to handle *other* threads doing stores (with that
> smp_store_release() in seccomp_sync_threads()).  Incidentally, this
>         if (!lock_task_sighand(task, &flags))
>                 return -ESRCH;
>
>         f = READ_ONCE(task->seccomp.filter);
> in proc_pid_seccomp_cache() looks cargo-culted - it's *not* a lockless
> access, so this READ_ONCE() is confusing.

> Kees, is there any reason not to make it a plain int?  And what is
> that READ_ONCE() doing in proc_pid_seccomp_cache(), while we are
> at it...  That's 0d8315dddd28 "seccomp/cache: Report cache data
> through /proc/pid/seccomp_cache", by YiFei Zhu <yifeifz2@...inois.edu>,
> AFAICS.  Looks like YiFei Zhu <zhuyifei@...gle.com> is the current
> address [Cc'd]...

I don't remember the context, but looking at the lore [1], AFAICT, it
was initially incorrectly lockless, then locking was added; READ_ONCE
was a missed leftover.

Can send a patch to remove it.

YiFei Zhu

[1] https://lore.kernel.org/all/CAG48ez0whaSTobwnoJHW+Eyqg5a8H4JCO-KHrgsuNiEg0qbD3w@mail.gmail.com/