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SubjectRe: For review: seccomp_user_notif(2) manual page
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Hello Kees,

On 10/1/20 1:39 AM, Kees Cook wrote:
> On Wed, Sep 30, 2020 at 01:07:38PM +0200, Michael Kerrisk (man-pages) wrote:
>> [...] I did :-)
>
> Yay! Thank you!

You're welcome :-)

>> [...]
>> Overview
>> In conventional usage of a seccomp filter, the decision about how
>> to treat a particular system call is made by the filter itself.
>> The user-space notification mechanism allows the handling of the
>> system call to instead be handed off to a user-space process.
>> The advantages of doing this are that, by contrast with the sec‐
>> comp filter, which is running on a virtual machine inside the
>> kernel, the user-space process has access to information that is
>> unavailable to the seccomp filter and it can perform actions that
>> can't be performed from the seccomp filter.
>
> I might clarify a bit with something like (though maybe the
> target/supervisor paragraph needs to be moved to the start):
>
> This is used for performing syscalls on behalf of the target,
> rather than having the supervisor make security policy decisions
> about the syscall, which would be inherently race-prone. The
> target's syscall should either be handled by the supervisor or
> allowed to continue normally in the kernel (where standard security
> policies will be applied).

You, Christian, and Jann all pulled me up on this point. And thanks;
I'm going to use some of your words above. See my reply to Jann, sent
at about the same time as this reply. Please take a look at the text
in my reply to Jann, and let me know what you think.

> I'll comment more later, but I've run out of time today and I didn't see
> anyone mention this detail yet in the existing threads... :)

Later never came :-). But, I hope you may have comments for the
next draft, which I will send out soon.

Thanks,

Michael

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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