Re: [PATCH v3] scripts/selinux: modernize mdp

[Stephen Smalley <stephen.smalley@gmail.com>]

On Wed, Feb 20, 2019 at 10:34 AM Dominick Grift
<dominick.grift@defensec.nl> wrote:
>
> The MDP example no longer works on modern systems.
>
> Add support for devtmpfs. This is required by login programs to relabel terminals.
> Compile the policy with deny_unknown allow status to anticipate user space object managers in core components such as systemd.
> Add default seusers mapping and failsafe context for the SELinux PAM module.
>
> V2:
> Fix existing file test for setfiles.
> Add a file test for checkpolicy similar to the test for setfiles for consistency.
> Execute setfiles with -F to ensure that customizables are relabeled as well in scenarios where filesystems are labeled but where SELinux is disabled.
>
> V3: Fixes file test that was introduced in V2.
>
> Signed-off-by: Dominick Grift <dominick.grift@defensec.nl>
> ---
>  scripts/selinux/install_policy.sh | 21 ++++++++++++++++-----
>  scripts/selinux/mdp/mdp.c         |  1 +
>  2 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/selinux/install_policy.sh b/scripts/selinux/install_policy.sh
> index 0b86c47baf7d..e32f333f14cc 100755
> --- a/scripts/selinux/install_policy.sh
> +++ b/scripts/selinux/install_policy.sh
> @@ -6,7 +6,7 @@ if [ `id -u` -ne 0 ]; then
>  fi
>  SF=`which setfiles`
>  if [ $? -eq 1 ]; then
> -       if [ -f /sbin/setfiles ]; then
> +       if [ -f /usr/setfiles ]; then
>                 SF="/usr/setfiles"

I don't believe we've ever installed setfiles anywhere other than
/sbin/setfile or /usr/sbin/setfiles so no other locations should be
used.  Maybe just drop the inner if statement entirely.

>         else
>                 echo "no selinux tools installed: setfiles"
> @@ -17,14 +17,25 @@ fi
>  cd mdp
>
>  CP=`which checkpolicy`
> +if [ $? -eq 1 ]; then
> +       if [ -f /usr/checkpolicy ]; then
> +               CP="/usr/checkpolicy"

Similarly for /usr/bin/checkpolicy or /bin/checkpolicy.

> +       else
> +               echo "no selinux tools installed: checkpolicy"
> +               exit 1
> +       fi
> +fi
>  VERS=`$CP -V | awk '{print $1}'`
>
>  ./mdp policy.conf file_contexts
> -$CP -o policy.$VERS policy.conf
> +$CP -U allow -o policy.$VERS policy.conf
>
>  mkdir -p /etc/selinux/dummy/policy
>  mkdir -p /etc/selinux/dummy/contexts/files
>
> +echo "__default__:user_u" > /etc/selinux/dummy/seusers
> +echo "base_r:base_t" > /etc/selinux/dummy/contexts/failsafe_context
> +
>  cp file_contexts /etc/selinux/dummy/contexts/files
>  cp dbus_contexts /etc/selinux/dummy/contexts
>  cp policy.$VERS /etc/selinux/dummy/policy
> @@ -55,15 +66,15 @@ else
>  fi
>
>  cd /etc/selinux/dummy/contexts/files
> -$SF file_contexts /
> +$SF -F file_contexts /
>
>  mounts=`cat /proc/$$/mounts | egrep "ext2|ext3|xfs|jfs|ext4|ext4dev|gfs2" | awk '{ print $2 '}`
> -$SF file_contexts $mounts
> +$SF -F file_contexts $mounts
>
>
>  dodev=`cat /proc/$$/mounts | grep "/dev "`
>  if [ "eq$dodev" != "eq" ]; then
>         mount --move /dev /mnt

I recall seeing errors from mount when running this script about
invalid usage of mount --move?

> -       $SF file_contexts /dev
> +       $SF -F file_contexts /dev
>         mount --move /mnt /dev
>  fi
> diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
> index 073fe7537f6c..cf06d5694cbc 100644
> --- a/scripts/selinux/mdp/mdp.c
> +++ b/scripts/selinux/mdp/mdp.c
> @@ -131,6 +131,7 @@ int main(int argc, char *argv[])
>
>         fprintf(fout, "fs_use_trans mqueue user_u:base_r:base_t;\n");
>         fprintf(fout, "fs_use_trans devpts user_u:base_r:base_t;\n");
> +       fprintf(fout, "fs_use_trans devtmpfs user_u:base_r:base_t;\n");

This will conflict with my patch but probably your patch should be
applied first since it fixes current usage of mdp, and then mine can
be re-based and introduce the MLS support (which hopefully can now be
tested on Fedora). Ideally we'd add fs_use* and genfscon statements
for all filesystems supported by the kernel but that can come later.

>         fprintf(fout, "fs_use_trans hugetlbfs user_u:base_r:base_t;\n");
>         fprintf(fout, "fs_use_trans tmpfs user_u:base_r:base_t;\n");
>         fprintf(fout, "fs_use_trans shm user_u:base_r:base_t;\n");
> --
> 2.21.0.rc1
>