linux-kernel - Re: [PATCH] audit: do a quick exit when syscall number is invalid

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Message-ID: <CAHC9VhTLTQmHaka9tTyuu=rQOzpsn_K2NxfJ==7-6FSY3KnuFg@mail.gmail.com>
Date:   Tue, 29 Mar 2022 09:11:19 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     CGEL <cgel.zte@...il.com>
Cc:     rth@...ddle.net, ink@...assic.park.msu.ru, mattst88@...il.com,
        eparis@...hat.com, linux-audit@...hat.com, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Yang Yang <yang.yang29@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] audit: do a quick exit when syscall number is invalid

On Mon, Mar 28, 2022 at 11:22 PM CGEL <cgel.zte@...il.com> wrote:
> On Mon, Mar 28, 2022 at 11:06:12PM -0400, Paul Moore wrote:
> > On Mon, Mar 28, 2022 at 9:48 PM CGEL <cgel.zte@...il.com> wrote:
> > > Sorry could anybody give a hand to solve this? It works well on x86_64 and arm64.
> > > I have no alpha environment and not familiar to this arch, much thanks!
> >
> > Regardless of if this is fixed, I'm not convinced this is something we
> > want to merge.  After all, a process executed a syscall and we should
> > process it like any other; just because it happens to be an
> > unrecognized syscall on a particular kernel build doesn't mean it
> > isn't security relevant (probing for specific syscall numbers may be a
> > useful attack fingerprint).
>
> Thanks for your reply.
>
> But syscall number less than 0 is even invalid for auditctl. So we
> will never hit this kind of audit rule. And invalid syscall number
> will always cause failure early in syscall handle.
>
> sh-4.2# auditctl -a always,exit -F arch=b64 -S -1
> Syscall name unknown: -1

You can add an audit filter without explicitly specifying a syscall:

% auditctl -a exit,always -F auid=1000
% auditctl -l
-a always,exit -S all -F auid=1000

-- 
paul-moore.com