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

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Date:   Thu, 31 Mar 2022 02:29:47 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Paul Moore <paul@...l-moore.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>, guo.xiaofeng@....com.cn,
        huang.junhua@....com.cn, dai.shixin@....com.cn
Subject: Re: [PATCH] audit: do a quick exit when syscall number is invalid

On Wed, Mar 30, 2022 at 10:48:12AM -0400, Paul Moore wrote:
> On Wed, Mar 30, 2022 at 1:59 AM CGEL <cgel.zte@...il.com> wrote:
> > On Tue, Mar 29, 2022 at 09:11:19AM -0400, Paul Moore wrote:
> > > 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
> > >
> > I have tried this, and execute program which call syscall number is -1,
> > audit still didn't record it. It supports that there's no need for audit
> > to handle syscall number less than 0.
> >
> > sh-4.2# auditctl -a exit,always
> > sh-4.2# auditctl -l
> > -a always,exit -S all
> 
> If audit is not generating SYSCALL records, even for invalid/ENOSYS
> syscalls, I would consider that a bug which should be fixed.
>
If we fix this bug, do you think audit invalid/ENOSYS syscalls better
be forcible or be a rule that can be configure? I think configure is 
better.
> -- 
> paul-moore.com