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Date:   Mon, 10 Oct 2022 18:44:33 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     John Johansen <john.johansen@...onical.com>,
        netdev@...r.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr_t safe

On Mon, Oct 10, 2022 at 6:39 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 10/10/2022 3:00 PM, Paul Moore wrote:
> > On Mon, Oct 10, 2022 at 5:58 PM Paul Moore <paul@...l-moore.com> wrote:
> >> Commit 4ff09db1b79b ("bpf: net: Change sk_getsockopt() to take the
> >> sockptr_t argument") made it possible to call sk_getsockopt()
> >> with both user and kernel address space buffers through the use of
> >> the sockptr_t type.  Unfortunately at the time of conversion the
> >> security_socket_getpeersec_stream() LSM hook was written to only
> >> accept userspace buffers, and in a desire to avoid having to change
> >> the LSM hook the commit author simply passed the sockptr_t's
> >> userspace buffer pointer.  Since the only sk_getsockopt() callers
> >> at the time of conversion which used kernel sockptr_t buffers did
> >> not allow SO_PEERSEC, and hence the
> >> security_socket_getpeersec_stream() hook, this was acceptable but
> >> also very fragile as future changes presented the possibility of
> >> silently passing kernel space pointers to the LSM hook.
> >>
> >> There are several ways to protect against this, including careful
> >> code review of future commits, but since relying on code review to
> >> catch bugs is a recipe for disaster and the upstream eBPF maintainer
> >> is "strongly against defensive programming", this patch updates the
> >> LSM hook, and all of the implementations to support sockptr_t and
> >> safely handle both user and kernel space buffers.
> >>
> >> Signed-off-by: Paul Moore <paul@...l-moore.com>
> >> ---
> >>  include/linux/lsm_hook_defs.h |    2 +-
> >>  include/linux/lsm_hooks.h     |    4 ++--
> >>  include/linux/security.h      |   11 +++++++----
> >>  net/core/sock.c               |    3 ++-
> >>  security/apparmor/lsm.c       |   29 +++++++++++++----------------
> >>  security/security.c           |    6 +++---
> >>  security/selinux/hooks.c      |   13 ++++++-------
> >>  security/smack/smack_lsm.c    |   19 ++++++++++---------
> >>  8 files changed, 44 insertions(+), 43 deletions(-)
> > Casey and John, could you please look over the Smack and AppArmor bits
> > of this patch when you get a chance?  I did my best on the conversion,
> > but I would appreciate a review by the experts :)
>
> I'm off the grid until 10/20, but will add this to my do-asap stack.

No worries, this is linux-next stuff anyway so no real rush at this
point.  Enjoy the time away.

-- 
paul-moore.com

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