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

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Message-ID: <831c2cad-c929-4190-8c79-da8192124a9c@oracle.com>
Date: Thu, 4 Sep 2025 12:10:32 -0600
From: Tom Hromatka <tom.hromatka@...cle.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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 9/4/25 8:54 AM, Al Viro wrote:
> On Thu, Sep 04, 2025 at 08:26:30AM -0600, Tom Hromatka wrote:
> 
>> This snippet addresses the double irq issue.  I also added a
>> check to make sure that task != current.  (A user shouldn't
>> do that but who knows what they'll actually do.)
>>
>>          if (task == current) {
>>                  put_task_struct(task);
>>                  return -EINVAL;
>>          }
>>
>>          spin_lock_irq(&current->sighand->siglock);
>>          spin_lock(&task->sighand->siglock);
> 
> What do you expect to happen if two tasks do that to each other
> at the same time? 

As written, they'll deadlock sooner or later :(.

But that should be easy to fix by adding two checks prior to
grabbing locks:
1.  Check that the source has 1 or more seccomp filters
2.  Check that the target has 0 seccomp filters.

This would ensure that for the same two processes, there's
only one way the locks could be grabbed.


> Or, for that matter, if task has been spawned
> by current with CLONE_VM | CLONE_SIGHAND?

Don't know right off hand.  I'll look into it.

Thanks for the help!

Tom