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From:   Kees Cook <keescook@chromium.org>
Date:   Fri, 15 Mar 2019 22:38:28 -0700
Message-ID: <CAGXu5jL-e7bDEXfpUuT-HyFarR-8T0djXChR0cuzTwFQPQ0tOw@mail.gmail.com>
Subject: Re: mount.nfs: Protocol error after upgrade to linux/master
To:     Jakub Kicinski <jakub.kicinski@netronome.com>,
        linux-security-module <linux-security-module@vger.kernel.org>
Cc:     Trond Myklebust <trond.myklebust@hammerspace.com>,
        "open list:NFS, SUNRPC, AND..." <linux-nfs@vger.kernel.org>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        LKML <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, Mar 15, 2019 at 10:24 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Mar 15, 2019 at 4:54 PM Jakub Kicinski
> <jakub.kicinski@netronome.com> wrote:
> >
> > On Fri, 15 Mar 2019 12:01:05 -0700, Jakub Kicinski wrote:
> > > On Fri, 15 Mar 2019 11:05:55 -0700, Jakub Kicinski wrote:
> > > > Hi,
> > > >
> > > > I just upgraded from:
> > > >
> > > > commit a3b1933d34d5bb26d7503752e3528315a9e28339 (net)
> > > > Merge: c6873d18cb4a 24319258660a
> > > > Author: David S. Miller <davem@davemloft.net>
> > > > Date:   Mon Mar 11 16:22:49 2019 -0700
> > > >
> > > > to
> > > >
> > > > commit 3b319ee220a8795406852a897299dbdfc1b09911
> > > > Merge: 9352ca585b2a b6e88119f1ed
> > > > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > > > Date:   Thu Mar 14 10:48:14 2019 -0700
> > > >
> > > > and I'm seeing:
> > > >
> > > > # mount /home/
> > > > mount.nfs: Protocol error
> > > >
> > > > No errors in dmesg, please let me know if it's a known problem or what
> > > > other info could be of use.
> > >
> > > Hm.. I tried to bisect but reverting to that commit doesn't help.
> > >
> > > Looks like the server responds with:
> > >
> > >   ICMP parameter problem - octet 22, length 80
> > >
> > > pointing at some IP options (type 134)...
> >
> > Okay, figured it out, it's the commit 13e735c0e953 ("LSM: Introduce
> > CONFIG_LSM") and all the related changes in security/
> >
> > I did olddefconfig and it changed my security module from apparmor to
> > smack silently.  smack must be slapping those IP options on by default.
> >
> > Pretty awful user experience, and a non-zero chance that users who
> > upgrade their kernels will miss this and end up with the wrong security
> > module...
>
> I wonder if we can add some kind of logic to Kconfig to retain the old
> CONFIG_DEFAULT_SECURITY and include it as the first legacy-major LSM
> listed in CONFIG_LSM?
>
> Like, but the old selector back in, but mark is as "soon to be
> entirely replaced with CONFIG_LSM" and then make CONFIG_LSM's default
> be "yama,loadpin,safesetid,integrity,$(CONFIG_DEFAULT_SECURITY),selinux,smack,tomoyo,apparmor"
> ? Duplicates are ignored...

This would initialize a default order from the earlier Kconfig items:

diff --git a/security/Kconfig b/security/Kconfig
index 1d6463fb1450..e3813b5c6824 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -239,8 +239,40 @@ source "security/safesetid/Kconfig"

 source "security/integrity/Kconfig"

+choice
+       prompt "First legacy-major LSM to be initialized"
+       default DEFAULT_SECURITY_SELINUX if SECURITY_SELINUX
+       default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
+       default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
+       default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
+       default DEFAULT_SECURITY_DAC
+
+       help
+         Select the legacy-major security module that will be initialize
+         first. Overridden by non-default CONFIG_LSM.
+
+       config DEFAULT_SECURITY_SELINUX
+               bool "SELinux" if SECURITY_SELINUX=y
+
+       config DEFAULT_SECURITY_SMACK
+               bool "Simplified Mandatory Access Control" if SECURITY_SMACK=y
+
+       config DEFAULT_SECURITY_TOMOYO
+               bool "TOMOYO" if SECURITY_TOMOYO=y
+
+       config DEFAULT_SECURITY_APPARMOR
+               bool "AppArmor" if SECURITY_APPARMOR=y
+
+       config DEFAULT_SECURITY_DAC
+               bool "Unix Discretionary Access Controls"
+
+endchoice
+
 config LSM
        string "Ordered list of enabled LSMs"
+       default
"yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if
DEFAULT_SECURITY_SMACK
+       default
"yama,loadpin,safesetid,integrity,tomoyo,selinux,smack,apparmor" if
DEFAULT_SECURITY_TOMOYO
+       default
"yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if
DEFAULT_SECURITY_APPARMOR
        default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
        help
          A comma-separated list of LSMs, in initialization order.

(I don't see a way to include an earlier config string in a new
default.) Thoughts?

-- 
Kees Cook