lkml.org 
[lkml]   [2020]   [Jan]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI)
    On 10-Jan 06:07, James Morris wrote:
    > On Thu, 9 Jan 2020, Stephen Smalley wrote:
    >
    > > On 1/9/20 1:11 PM, James Morris wrote:
    > > > On Wed, 8 Jan 2020, Stephen Smalley wrote:
    > > >
    > > > > The cover letter subject line and the Kconfig help text refer to it as a
    > > > > BPF-based "MAC and Audit policy". It has an enforce config option that
    > > > > enables the bpf programs to deny access, providing access control. IIRC,
    > > > > in
    > > > > the earlier discussion threads, the BPF maintainers suggested that Smack
    > > > > and
    > > > > other LSMs could be entirely re-implemented via it in the future, and that
    > > > > such an implementation would be more optimal.
    > > >
    > > > In this case, the eBPF code is similar to a kernel module, rather than a
    > > > loadable policy file. It's a loadable mechanism, rather than a policy, in
    > > > my view.
    > >
    > > I thought you frowned on dynamically loadable LSMs for both security and
    > > correctness reasons?

    Based on the feedback from the lists we've updated the design for v2.

    In v2, LSM hook callbacks are allocated dynamically using BPF
    trampolines, appended to a separate security_hook_heads and run
    only after the statically allocated hooks.

    The security_hook_heads for all the other LSMs (SELinux, AppArmor etc)
    still remains __lsm_ro_after_init and cannot be modified. We are still
    working on v2 (not ready for review yet) but the general idea can be
    seen here:

    https://github.com/sinkap/linux-krsi/blob/patch/v1/trampoline_prototype/security/bpf/lsm.c

    >
    > Evaluating the security impact of this is the next step. My understanding
    > is that eBPF via BTF is constrained to read only access to hook
    > parameters, and that its behavior would be entirely restrictive.
    >
    > I'd like to understand the security impact more fully, though. Can the
    > eBPF code make arbitrary writes to the kernel, or read anything other than
    > the correctly bounded LSM hook parameters?
    >

    As mentioned, the BPF verifier does not allow writes to BTF types.

    > > And a traditional security module would necessarily fall
    > > under GPL; is the eBPF code required to be likewise? If not, KRSI is a
    > > gateway for proprietary LSMs...
    >
    > Right, we do not want this to be a GPL bypass.

    This is not intended to be a GPL bypass and the BPF verifier checks
    for license compatibility of the loaded program with GPL.

    - KP

    >
    > If these issues can be resolved, this may be a "safe" way to support
    > loadable LSM applications.
    >
    > Again, I'd be interested in knowing how this is is handled in the
    > networking stack (keeping in mind that LSM is a much more invasive API,
    > and may not be directly comparable).
    >
    > --
    > James Morris
    > <jmorris@namei.org>
    >

    \
     
     \ /
      Last update: 2020-01-09 20:43    [W:3.040 / U:0.076 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site