linux-kernel - Re: [RFC 1/1] seccomp: Add bitmask of allowed system calls.

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Message-ID: <20090508092039.GC3559@elte.hu>
Date:	Fri, 8 May 2009 11:20:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Adam Langley <agl@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, markus@...gle.com
Subject: Re: [RFC 1/1] seccomp: Add bitmask of allowed system calls.


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Thu, May 07, 2009 at 03:34:58PM -0700, Adam Langley wrote:
> > > That assessment is incorrect, there's no difference between safety
> > > here really.
> > >
> > > LSM cannot magically inspect user-space memory either when multiple
> > > threads may access it. The point would be to define filters for
> > > system call _arguments_, which are inherently thread-local and safe.
> > 
> > If I hook security_operations.socket_connect, I can validate the struct
> > sockaddr after the final copy_from_user. However, since the sockaddr lives in
> > userspace memory, if I try and validate it from ftrace SYSCALL_ENTER, I can't
> > know that it won't change before sys_connect reads it again.
> > 
> > Because of that, there are system calls which an LSM hook can safely accept
> > that an ftrace hook cannot. However, as you point out, any arguments passed in
> > registers are inheriently safe and these may be sufficiently powerful.
> > 
> > > There are two problems with the bitmap scheme, which i also
> > > suggested in a previous thread but then found it to be lacking:
> > >
> > > 1) enumeration: you define a bitmap. That will be problematic
> > >   between compat and native 64-bit (both have different syscall
> > >   vectors).
> > 
> > I /think/ it works out, but I've been bitten before with subtle 32/64 bit
> > compat issues and accept that it's a bit ugly.
> > 
> > > 2) flexibility. It's an on/off selection per syscall. With the
> > >   filter we have on, off, or filtered. That's a _whole_ lot more
> > >   flexible.
> > 
> > Absolutely.
> > 
> > Is there a git tree that I can pull this parsing code from?
> > (git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> > maybe?). I can patch in the seccomp-on-ftrace work and try building the
> > filtering on top of that. I'll see how it turns out anyway.
> 
> 
> Hi,
> 
> The most uptodate one is:
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git
> on the tracing/filters topic.
> 
> See kernel/trace/trace_events_filter.c

tracing/filters may lag behind - i'd suggest to use the master 
branch, that's the most stable stuff generally. Or tracing/core for 
any Git based tree.

	Ingo
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