netdev - Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr

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Message-ID: <CAHC9VhRfEiJunPo7bVzmPPg8UHDoFc0wvOhBaFrsLjfeDCg50g@mail.gmail.com>
Date:   Mon, 10 Oct 2022 18:00:38 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>
Cc:     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 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 :)

-- 
paul-moore.com