linux-kernel - Re: [PATCH] selinux: deprecated fs ocon

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Date:   Thu, 18 May 2023 13:56:25 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Christian Göttsche <cgzones@...glemail.com>,
        selinux@...r.kernel.org
Cc:     Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Xiu Jianfeng <xiujianfeng@...wei.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selinux: deprecated fs ocon

On May 11, 2023 =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgzones@...glemail.com> wrote:
> 
> The object context type `fs`, not to be confused with the well used
> object context type `fscon`, was introduced in the initial git commit
> 1da177e4c3f4 ("Linux-2.6.12-rc2") but never actually used since.
> 
> The paper "A Security Policy Configuration for the Security-Enhanced
> Linux" [1] mentions it under `7.2 File System Contexts` but also states:
> 
>     Currently, this configuration is unused.
> 
> The policy statement defining such object contexts is `fscon`, e.g.:
> 
>     fscon 2 3 gen_context(system_u:object_r:conA_t,s0) gen_context(system_u:object_r:conB_t,s0)
> 
> It is not documented at selinuxproject.org or in the SELinux notebook
> and not supported by the Reference Policy buildsystem - the statement is
> not properly sorted - and thus not used in the Reference or Fedora
> Policy.
> 
> Print a warning message at policy load for each such object context:
> 
>     SELinux:  void and deprecated fs ocon 02:03
> 
> This topic was initially highlighted by Nicolas Iooss [2].
> 
> [1]: https://media.defense.gov/2021/Jul/29/2002815735/-1/-1/0/SELINUX-SECURITY-POLICY-CONFIGURATION-REPORT.PDF
> [2]: https://lore.kernel.org/selinux/CAJfZ7=mP2eJaq2BfO3y0VnwUJaY2cS2p=HZMN71z1pKjzaT0Eg@mail.gmail.com/
> 
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> ---
>  security/selinux/ss/policydb.c | 4 ++++
>  security/selinux/ss/policydb.h | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)

Thanks, this is a nice catch, although some minor suggestions below ...

> diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
> index 97c0074f9312..31b08b34c722 100644
> --- a/security/selinux/ss/policydb.c
> +++ b/security/selinux/ss/policydb.c
> @@ -2257,6 +2257,10 @@ static int ocontext_read(struct policydb *p, const struct policydb_compat_info *
>  				if (rc)
>  					goto out;
>  
> +				if (i == OCON_FS)
> +					pr_warn("SELinux:  void and deprecated fs ocon %s\n",
> +						c->u.name);

Instead of having to check if 'i == OCON_FS', why not simply put the
pr_warn() call up in the OCON_FS case block on line ~2249 and let it
continue to fallthrough to the OCON_NETIF block?

>  				rc = context_read_and_validate(&c->context[0], p, fp);
>  				if (rc)
>  					goto out;
> diff --git a/security/selinux/ss/policydb.h b/security/selinux/ss/policydb.h
> index ffc4e7bad205..39cd6222e1a8 100644
> --- a/security/selinux/ss/policydb.h
> +++ b/security/selinux/ss/policydb.h
> @@ -225,7 +225,7 @@ struct genfs {
>  
>  /* object context array indices */
>  #define OCON_ISID	0 /* initial SIDs */
> -#define OCON_FS		1 /* unlabeled file systems */
> +#define OCON_FS		1 /* unlabeled file systems (deprecated in 6.5) */

Since you are likely re-spinning this (see above), I would just leave
it as "(deprecated)"; those that want to know where it was deprecated
can always check the git log/tags.

>  #define OCON_PORT	2 /* TCP and UDP port numbers */
>  #define OCON_NETIF	3 /* network interfaces */
>  #define OCON_NODE	4 /* nodes */
> -- 
> 2.40.1

--
paul-moore.com