Re: [PATCH v15 18/23] NET: Store LSM netlabel data in a lsmblob

From: Paul Moore <paul@paul-moore.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: casey.schaufler@intel.com, James Morris <jmorris@namei.org>,
	linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	keescook@chromium.org, john.johansen@canonical.com,
	penguin-kernel@i-love.sakura.ne.jp,
	Stephen Smalley <sds@tycho.nsa.gov>
Subject: Re: [PATCH v15 18/23] NET: Store LSM netlabel data in a lsmblob
Date: Fri, 6 Mar 2020 21:14:35 -0500	[thread overview]
Message-ID: <CAHC9VhREcdFNtJkXkUrwtbu8GA_h2T5CJ9hAQCU0PSpd5yLGgg@mail.gmail.com> (raw)
In-Reply-To: <20200214234203.7086-19-casey@schaufler-ca.com>

On Fri, Feb 14, 2020 at 6:45 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> Netlabel uses LSM interfaces requiring an lsmblob and
> the internal storage is used to pass information between
> these interfaces, so change the internal data from a secid
> to a lsmblob. Update the netlabel interfaces and their
> callers to accommodate the change. This requires that the
> modules using netlabel use the lsm_id.slot to access the
> correct secid when using netlabel.
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: John Johansen <john.johansen@canonical.com>
> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  include/net/netlabel.h              |  8 ++--
>  net/ipv4/cipso_ipv4.c               | 23 +++++++-----
>  net/netlabel/netlabel_kapi.c        |  6 +--
>  net/netlabel/netlabel_unlabeled.c   | 57 +++++++++++------------------
>  net/netlabel/netlabel_unlabeled.h   |  2 +-
>  security/selinux/hooks.c            |  2 +-
>  security/selinux/include/security.h |  1 +
>  security/selinux/netlabel.c         |  2 +-
>  security/selinux/ss/services.c      |  4 +-
>  security/smack/smack.h              |  1 +
>  security/smack/smack_lsm.c          |  5 ++-
>  security/smack/smackfs.c            | 10 +++--
>  12 files changed, 59 insertions(+), 62 deletions(-)

...

> diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
> index 376882215919..adb9dffc3952 100644
> --- a/net/ipv4/cipso_ipv4.c
> +++ b/net/ipv4/cipso_ipv4.c
> @@ -106,15 +106,17 @@ int cipso_v4_rbm_strictvalid = 1;
>  /* Base length of the local tag (non-standard tag).
>   *  Tag definition (may change between kernel versions)
>   *
> - * 0          8          16         24         32
> - * +----------+----------+----------+----------+
> - * | 10000000 | 00000110 | 32-bit secid value  |
> - * +----------+----------+----------+----------+
> - * | in (host byte order)|
> - * +----------+----------+
> - *
> + * 0          8          16                    16 + sizeof(struct lsmblob)
> + * +----------+----------+---------------------+
> + * | 10000000 | 00000110 | LSM blob data       |
> + * +----------+----------+---------------------+
> + *
> + * All secid and flag fields are in host byte order.
> + * The lsmblob structure size varies depending on which
> + * Linux security modules are built in the kernel.
> + * The data is opaque.
>   */
> -#define CIPSO_V4_TAG_LOC_BLEN         6
> +#define CIPSO_V4_TAG_LOC_BLEN         (2 + sizeof(struct lsmblob))

This isn't as bad as the sk_buff.cb limitation so I'm not going to
worry too much about it, but just to be safe I think we should put a
compile-time check to ensure that the local tag is within the bounds
of the IPv4 option limit.  If we don't put a check I worry that there
is a chance someone could get a very rude surprise at some point in
the future (yes, this is highly unlikely, but still possible).

>  /*
>   * Helper Functions
> @@ -1467,7 +1469,8 @@ static int cipso_v4_gentag_loc(const struct cipso_v4_doi *doi_def,
>
>         buffer[0] = CIPSO_V4_TAG_LOCAL;
>         buffer[1] = CIPSO_V4_TAG_LOC_BLEN;
> -       *(u32 *)&buffer[2] = secattr->attr.secid;
> +       memcpy(&buffer[2], &secattr->attr.lsmblob,
> +              sizeof(secattr->attr.lsmblob));
>
>         return CIPSO_V4_TAG_LOC_BLEN;
>  }

-- 
paul moore
www.paul-moore.com