netdev - Re: [PATCH v12 07/13] seccomp: add SECCOMP_RET

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Message-Id: <1330981988.1484.9.camel@Nokia-N900-51-1>
Date:	Mon, 05 Mar 2012 15:13:08 -0600
From:	Serge Hallyn <serge@...lyn.com>
To:	Will Drewry <wad@...omium.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
	davem@...emloft.net, hpa@...or.com, mingo@...hat.com,
	oleg@...hat.com, peterz@...radead.org, rdunlap@...otime.net,
	mcgrathr@...omium.org, tglx@...utronix.de, luto@....edu,
	eparis@...hat.com, serge.hallyn@...onical.com, djm@...drot.org,
	scarybeasts@...il.com, indan@....nu, pmoore@...hat.com,
	akpm@...ux-foundation.org, corbet@....net, eric.dumazet@...il.com,
	markus@...omium.org, coreyb@...ux.vnet.ibm.com,
	keescook@...omium.org
Subject: Re: [PATCH v12 07/13] seccomp: add SECCOMP_RET_ERRNO


----- Original message -----
> On Fri, Mar 2, 2012 at 12:24 PM, Serge E. Hallyn <serge@...lyn.com>
> wrote:
> > Quoting Will Drewry (wad@...omium.org):
> > > This change adds the SECCOMP_RET_ERRNO as a valid return value from a
> > > seccomp filter.  Additionally, it makes the first use of the lower
> > > 16-bits for storing a filter-supplied errno.  16-bits is more than
> > > enough for the errno-base.h calls.
> > > 
> > > Returning errors instead of immediately terminating processes that
> > > violate seccomp policy allow for broader use of this functionality
> > > for kernel attack surface reduction.  For example, a linux container
> > > could maintain a whitelist of pre-existing system calls but drop
> > > all new ones with errnos.  This would keep a logically static attack
> > > surface while providing errnos that may allow for graceful failure
> > > without the downside of do_exit() on a bad call.
> > > 
> > > v12: - move to WARN_ON if filter is NULL
> > >        (oleg@...hat.com, luto@....edu, keescook@...omium.org)
> > >      - return immediately for filter==NULL (keescook@...omium.org)
> > >      - change evaluation to only compare the ACTION so that layered
> > >        errnos don't result in the lowest one being returned.
> > >        (keeschook@...omium.org)
> > > v11: - check for NULL filter (keescook@...omium.org)
> > > v10: - change loaders to fn
> > >  v9: - n/a
> > >  v8: - update Kconfig to note new need for syscall_set_return_value.
> > >      - reordered such that TRAP behavior follows on later.
> > >      - made the for loop a little less indent-y
> > >  v7: - introduced
> > > 
> > > Reviewed-by: Kees Cook <keescook@...omium.org>
> > > Signed-off-by: Will Drewry <wad@...omium.org>
> > 
> > Clever :)
> > 
> > Thanks, Will.
> > 
> > For patches 1-7,
> > 
> > Acked-by: Serge Hallyn <serge.hallyn@...onical.com>
> 
> Thanks!
> 
> > The -1 return value from __secure_computing_int() seems like it
> > could stand  #define, like
> > 
> > #define SECCOMP_DONTRUN -1
> > #define SECCOMP_RUN 0
> > 
> > or something Maybe not, but -1 always scares me and I had to look back
> > and forth a few times to make sure it was doing what I would want.
> 
> Works for me.   The -1 just matches what syscall emulation, etc does on
> x86.   I'll add this to the tweaks for v14.
> 
> Thanks!

Well, in that case maybe it's not worth it.  Sounds
like ignorance on my part.

thanks,
-serge
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