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

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Message-ID: <CAHC9VhTOQpk8oqyg_1Vh8QDjsMwJC6A-K7tTgRVYBB6ckqJ9qg@mail.gmail.com>
Date:   Sat, 2 Apr 2022 11:07:57 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     CGEL <cgel.zte@...il.com>
Cc:     Steve Grubb <sgrubb@...hat.com>, linux-audit@...hat.com,
        kbuild-all@...ts.01.org, Zeal Robot <zealci@....com.cn>,
        linux-kernel@...r.kernel.org, eparis@...hat.com,
        dai.shixin@....com.cn, Yang Yang <yang.yang29@....com.cn>,
        ink@...assic.park.msu.ru, huang.junhua@....com.cn,
        guo.xiaofeng@....com.cn, mattst88@...il.com
Subject: Re: [PATCH] audit: do a quick exit when syscall number is invalid

On Sat, Apr 2, 2022 at 4:06 AM CGEL <cgel.zte@...il.com> wrote:
> On Fri, Apr 01, 2022 at 10:16:45AM -0400, Paul Moore wrote:
> > On Fri, Apr 1, 2022 at 9:39 AM Steve Grubb <sgrubb@...hat.com> wrote:
> > >
> > > On Thursday, March 31, 2022 9:57:05 PM EDT CGEL wrote:
> > > > On Thu, Mar 31, 2022 at 10:16:23AM -0400, Paul Moore wrote:
> > > > > On Wed, Mar 30, 2022 at 10:29 PM CGEL <cgel.zte@...il.com> wrote:
> > > > > > On Wed, Mar 30, 2022 at 10:48:12AM -0400, Paul Moore wrote:
> > > > > > > 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.
> > > > >
> > > > > It isn't clear to me exactly what you are asking, but I would expect
> > > > > the existing audit syscall filtering mechanism to work regardless if
> > > > > the syscall is valid or not.
> > > >
> > > > Thanks, I try to make it more clear. We found that auditctl would only
> > > > set rule with syscall number (>=0 && <2047) ...
> >
> > That is exactly why I wrote the warning below in my response ...
> >
> I think the question is more clear now.
>
> 1) libaudit.c wants to forbid setting invalid syscall, but inconsistent
> Currently way(>=0 && <2047) is inconsistent, syscall with number 2000 and
> syscall with number 3000 are both invalid syscall. But 2000 can be set by
> auditctl, and 3000 cannot be set by auditctl.
> A better way to do this forbidden is to use __NR_syscalls(asm-generic/unistd.h).
>
> 2) if libaudit.c do the right forbidden, kernel better ignore invalid syscall
> See this patch.
>
> If we want audit invalid syscall as you said before. libaudit.c should not
> do the forbidden, auditctl should allow setting syscall rule with 'any' number.
> So do you think we should fix libaudit.c?

I'm really not very clear on what you are proposing, but we can't
change the kernel/userspace API in any way which would break
compatibility with old/existing userspace tools.

-- 
paul-moore.com