Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)

From: Loganaden Velvindron <loganaden@gmail.com>
To: David Drysdale <drysdale@google.com>
Cc: Andi Kleen <andi@firstfloor.org>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Meredydd Luff <meredydd@senatehouse.org>,
	Kees Cook <keescook@chromium.org>,
	James Morris <james.l.morris@oracle.com>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)
Date: Tue, 1 Jul 2014 22:58:16 +0400	[thread overview]
Message-ID: <CAOp4FwR3Wn0=8ZdButz6QquaDO5RABTcfB3+TVjjZ1aYV7X8wQ@mail.gmail.com> (raw)
In-Reply-To: <20140701095356.GC2242@google.com>

On Tue, Jul 1, 2014 at 1:53 PM, David Drysdale <drysdale@google.com> wrote:
> On Mon, Jun 30, 2014 at 01:40:40PM -0700, Andi Kleen wrote:
>> David Drysdale <drysdale@google.com> writes:
>>
>> > Add a new O_BENEATH_ONLY flag for openat(2) which restricts the
>> > provided path, rejecting (with -EACCES) paths that are not beneath
>> > the provided dfd.  In particular, reject:
>> >  - paths that contain .. components
>> >  - paths that begin with /
>> >  - symlinks that have paths as above.
>>
>> How about bind mounts?
>>
>> -Andi
>>
>> --
>> ak@linux.intel.com -- Speaking for myself only
>
> Bind mounts won't get rejected because they just look like normal
> path components.  In other words, if dir/subdir is a bind mount to
> /root/dir then:
>   fd = openat(AT_FDCWD, "dir/subdir", O_RDONLY|O_BENEATH_ONLY);
> will work fine.

Talking about David's efforts at porting Capsicum to Linux, I've
already implemented
support for Capsicum in OpenSSH. It shouldn't be complicated to enable
it on Linux
systems that support it.

I would very like to see capsicum integrated into mainline, as it's a
high quality sandbox
solution, that will benefit a lot of server software that implement
privilege separation.

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