Re: [PATCH] scripts/selinux: modernize mdp

[Dominick Grift <dominick.grift@defensec.nl>]

On Thu, Feb 21, 2019 at 01:42:13PM -0500, Stephen Smalley wrote:
> Derived in part from a patch by Dominick Grift.
> 
> The MDP example no longer works on modern systems.  Fix it.
> While we are at it, add MLS support and enable it.
> 
> NB This still does not work on systems using dbus-daemon instead of
> dbus-broker because dbus-daemon does not yet gracefully handle unknown
> classes/permissions.  This is a deficiency in libselinux's
> selinux_set_mapping() interface and underlying implementation,
> which was never fully updated to deal with unknown classes/permissions
> unlike the kernel.  Programs that instead use selinux_check_access()
> like dbus-broker do not have this problem.
> 
> Other known issues:
> - Not everything appears to be relabeled, so some files are left with invalid
> contexts and remapped to the unlabeled SID/context.
> - X will fail due to lack of a x_contexts file
> - libvirtd will fail due to lack of a virtual_domain_context file
> - crond reports an error with "No security context"
> 
> Changes to mdp:
> Add support for devtmpfs, required by modern Linux distributions.
> Add MLS support, with sample sensitivities, categories, and constraints.
> Generate fs_use and genfscon rules based on kernel configuration.
> Update list of filesystem types for fs_use and genfscon rules.
> Use object_r for object contexts.
> 
> Changes to install_policy.sh:
> Bail immediately on any errors.
> Provide more helpful error messages when unable to find userspace tools.
> Refuse to run if SELinux is already enabled.
> Unconditionally move aside /etc/selinux/config and create a new one.
> Build policy with -U allow so that userspace object managers do not break.
> Build policy with MLS enabled by default.
> Add default seusers mapping and failsafe context for use by
> pam_selinux / libselinux.
> Set to permissive mode rather than enforcing to permit initial autorelabel.
> Update the list of filesystem types to be relabeled.
> Create /.autorelabel to trigger an autorelabel on reboot.
> Drop broken attempt to relabel the /dev mountpoint directory.
> 
> Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
> ---
>  scripts/selinux/install_policy.sh |  82 ++++++++-------
>  scripts/selinux/mdp/mdp.c         | 164 +++++++++++++++++++++++++-----
>  2 files changed, 183 insertions(+), 63 deletions(-)
> 
> diff --git a/scripts/selinux/install_policy.sh b/scripts/selinux/install_policy.sh
> index 0b86c47baf7d..09eab4d0da5c 100755
> --- a/scripts/selinux/install_policy.sh
> +++ b/scripts/selinux/install_policy.sh
> @@ -1,30 +1,51 @@
>  #!/bin/sh
>  # SPDX-License-Identifier: GPL-2.0
> +set -e
>  if [ `id -u` -ne 0 ]; then
>  	echo "$0: must be root to install the selinux policy"
>  	exit 1
>  fi
> +
>  SF=`which setfiles`
>  if [ $? -eq 1 ]; then
> -	if [ -f /sbin/setfiles ]; then
> -		SF="/usr/setfiles"
> -	else
> -		echo "no selinux tools installed: setfiles"
> -		exit 1
> -	fi
> +	echo "Could not find setfiles"
> +	echo "Do you have policycoreutils installed?"
> +	exit 1
>  fi
>  
> -cd mdp
> -
>  CP=`which checkpolicy`
> +if [ $? -eq 1 ]; then
> +	echo "Could not find checkpolicy"
> +	echo "Do you have checkpolicy installed?"
> +	exit 1
> +fi
>  VERS=`$CP -V | awk '{print $1}'`
>  
> -./mdp policy.conf file_contexts
> -$CP -o policy.$VERS policy.conf
> +ENABLED=`which selinuxenabled`
> +if [ $? -eq 1 ]; then
> +	echo "Could not find selinuxenabled"
> +	echo "Do you have libselinux-utils installed?"
> +	exit 1
> +fi
> +
> +if selinuxenabled; then
> +    echo "SELinux is already enabled"
> +    echo "This prevents safely relabeling all files."
> +    echo "Boot with selinux=0 on the kernel command-line or"
> +    echo "SELINUX=disabled in /etc/selinux/config."
> +    exit 1
> +fi
> +
> +cd mdp
> +./mdp -m policy.conf file_contexts
> +$CP -U allow -M -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

Should this be "__default__:user_u:s0-s0"?

> +echo "base_r:base_t" > /etc/selinux/dummy/contexts/failsafe_context

Should this be "base_r:base_t:s0"?

> +
>  cp file_contexts /etc/selinux/dummy/contexts/files
>  cp dbus_contexts /etc/selinux/dummy/contexts
>  cp policy.$VERS /etc/selinux/dummy/policy
> @@ -33,37 +54,22 @@ FC_FILE=/etc/selinux/dummy/contexts/files/file_contexts
>  if [ ! -d /etc/selinux ]; then
>  	mkdir -p /etc/selinux
>  fi
> -if [ ! -f /etc/selinux/config ]; then
> -	cat > /etc/selinux/config << EOF
> -SELINUX=enforcing
> +if [ -f /etc/selinux/config ]; then
> +    echo "/etc/selinux/config exists, moving to /etc/selinux/config.bak."
> +    mv /etc/selinux/config /etc/selinux/config.bak
> +fi
> +echo "Creating new /etc/selinux/config for dummy policy."
> +cat > /etc/selinux/config << EOF
> +SELINUX=permissive
>  SELINUXTYPE=dummy
>  EOF
> -else
> -	TYPE=`cat /etc/selinux/config | grep "^SELINUXTYPE" | tail -1 | awk -F= '{ print $2 '}`
> -	if [ "eq$TYPE" != "eqdummy" ]; then
> -		selinuxenabled
> -		if [ $? -eq 0 ]; then
> -			echo "SELinux already enabled with a non-dummy policy."
> -			echo "Exiting.  Please install policy by hand if that"
> -			echo "is what you REALLY want."
> -			exit 1
> -		fi
> -		mv /etc/selinux/config /etc/selinux/config.mdpbak
> -		grep -v "^SELINUXTYPE" /etc/selinux/config.mdpbak >> /etc/selinux/config
> -		echo "SELINUXTYPE=dummy" >> /etc/selinux/config
> -	fi
> -fi
>  
>  cd /etc/selinux/dummy/contexts/files
> -$SF file_contexts /
> +$SF -F file_contexts /
>  
> -mounts=`cat /proc/$$/mounts | egrep "ext2|ext3|xfs|jfs|ext4|ext4dev|gfs2" | awk '{ print $2 '}`
> -$SF file_contexts $mounts
> +mounts=`cat /proc/$$/mounts | \
> +	egrep "ext[234]|jfs|xfs|reiserfs|jffs2|gfs2|btrfs|f2fs|ocfs2" | \
> +	awk '{ print $2 '}`
> +$SF -F file_contexts $mounts
>  
> -
> -dodev=`cat /proc/$$/mounts | grep "/dev "`
> -if [ "eq$dodev" != "eq" ]; then
> -	mount --move /dev /mnt
> -	$SF file_contexts /dev
> -	mount --move /mnt /dev
> -fi
> +touch /.autorelabel

Probably best to instead: "echo "-F" > /.autorelabel"?

> diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
> index 073fe7537f6c..daad333c7252 100644
> --- a/scripts/selinux/mdp/mdp.c
> +++ b/scripts/selinux/mdp/mdp.c
> @@ -33,6 +33,7 @@
>  #include <unistd.h>
>  #include <string.h>
>  #include <sys/socket.h>
> +#include <linux/kconfig.h>
>  
>  static void usage(char *name)
>  {
> @@ -95,10 +96,31 @@ int main(int argc, char *argv[])
>  	}
>  	fprintf(fout, "\n");
>  
> -	/* NOW PRINT OUT MLS STUFF */
> +	/* print out mls declarations and constraints */
>  	if (mls) {
> -		printf("MLS not yet implemented\n");
> -		exit(1);
> +		fprintf(fout, "sensitivity s0;\n");
> +		fprintf(fout, "sensitivity s1;\n");
> +		fprintf(fout, "dominance { s0 s1 }\n");
> +		fprintf(fout, "category c0;\n");
> +		fprintf(fout, "category c1;\n");
> +		fprintf(fout, "level s0:c0.c1;\n");
> +		fprintf(fout, "level s1:c0.c1;\n");
> +#define SYSTEMLOW "s0"
> +#define SYSTEMHIGH "s1:c0.c1"
> +		for (i = 0; secclass_map[i].name; i++) {
> +			struct security_class_mapping *map = &secclass_map[i];
> +
> +			fprintf(fout, "mlsconstrain %s {\n", map->name);
> +			for (j = 0; map->perms[j]; j++)
> +				fprintf(fout, "\t%s\n", map->perms[j]);
> +			/*
> +			 * This requires all subjects and objects to be
> +			 * single-level (l2 eq h2), and that the subject
> +			 * level dominate the object level (h1 dom h2)
> +			 * in order to have any permissions to it.
> +			 */
> +			fprintf(fout, "} (l2 eq h2 and h1 dom h2);\n\n");
> +		}
>  	}
>  
>  	/* types, roles, and allows */
> @@ -108,34 +130,126 @@ int main(int argc, char *argv[])
>  	for (i = 0; secclass_map[i].name; i++)
>  		fprintf(fout, "allow base_t base_t:%s *;\n",
>  			secclass_map[i].name);
> -	fprintf(fout, "user user_u roles { base_r };\n");
> -	fprintf(fout, "\n");
> +	fprintf(fout, "user user_u roles { base_r }");
> +	if (mls)
> +		fprintf(fout, " level %s range %s - %s", SYSTEMLOW,
> +			SYSTEMLOW, SYSTEMHIGH);
> +	fprintf(fout, ";\n");
> +
> +#define SUBJUSERROLETYPE "user_u:base_r:base_t"
> +#define OBJUSERROLETYPE "user_u:object_r:base_t"
>  
>  	/* default sids */
>  	for (i = 1; i < initial_sid_to_string_len; i++)
> -		fprintf(fout, "sid %s user_u:base_r:base_t\n", initial_sid_to_string[i]);
> +		fprintf(fout, "sid %s " SUBJUSERROLETYPE "%s\n",
> +			initial_sid_to_string[i], mls ? ":" SYSTEMLOW : "");
>  	fprintf(fout, "\n");
>  
> -	fprintf(fout, "fs_use_xattr ext2 user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr ext3 user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr ext4 user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr jfs user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr xfs user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr reiserfs user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr jffs2 user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_xattr gfs2 user_u:base_r:base_t;\n");
> +#define FS_USE(behavior, fstype)			    \
> +	fprintf(fout, "fs_use_%s %s " OBJUSERROLETYPE "%s;\n", \
> +		behavior, fstype, mls ? ":" SYSTEMLOW : "")
> +
> +	/*
> +	 * Filesystems whose inode labels can be fetched via getxattr.
> +	 */
> +#ifdef CONFIG_EXT2_FS_SECURITY
> +	FS_USE("xattr", "ext2");
> +#endif
> +#ifdef CONFIG_EXT3_FS_SECURITY
> +	FS_USE("xattr", "ext3");
> +#endif
> +#ifdef CONFIG_EXT4_FS_SECURITY
> +	FS_USE("xattr", "ext4");
> +#endif
> +#ifdef CONFIG_JFS_SECURITY
> +	FS_USE("xattr", "jfs");
> +#endif
> +#ifdef CONFIG_REISERFS_FS_SECURITY
> +	FS_USE("xattr", "reiserfs");
> +#endif
> +#ifdef CONFIG_JFFS2_FS_SECURITY
> +	FS_USE("xattr", "jffs2");
> +#endif
> +#ifdef CONFIG_XFS_FS
> +	FS_USE("xattr", "xfs");
> +#endif
> +#ifdef CONFIG_GFS2_FS
> +	FS_USE("xattr", "gfs2");
> +#endif
> +#ifdef CONFIG_BTRFS_FS
> +	FS_USE("xattr", "btrfs");
> +#endif
> +#ifdef CONFIG_F2FS_FS_SECURITY
> +	FS_USE("xattr", "f2fs");
> +#endif
> +#ifdef CONFIG_OCFS2_FS
> +	FS_USE("xattr", "ocsfs2");
> +#endif
> +#ifdef CONFIG_OVERLAY_FS
> +	FS_USE("xattr", "overlay");
> +#endif
> +#ifdef CONFIG_SQUASHFS_XATTR
> +	FS_USE("xattr", "squashfs");
> +#endif
> +
> +	/*
> +	 * Filesystems whose inodes are labeled from allocating task.
> +	 */
> +	FS_USE("task", "pipefs");
> +	FS_USE("task", "sockfs");
>  
> -	fprintf(fout, "fs_use_task eventpollfs user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_task pipefs user_u:base_r:base_t;\n");
> -	fprintf(fout, "fs_use_task sockfs user_u:base_r:base_t;\n");
> +	/*
> +	 * Filesystems whose inode labels are computed from both
> +	 * the allocating task and the superblock label.
> +	 */
> +#ifdef CONFIG_UNIX98_PTYS
> +	FS_USE("trans", "devpts");
> +#endif
> +#ifdef CONFIG_HUGETLBFS
> +	FS_USE("trans", "hugetlbfs");
> +#endif
> +#ifdef CONFIG_TMPFS
> +	FS_USE("trans", "tmpfs");
> +#endif
> +#ifdef CONFIG_DEVTMPFS
> +	FS_USE("trans", "devtmpfs");
> +#endif
> +#ifdef CONFIG_POSIX_MQUEUE
> +	FS_USE("trans", "mqueue");
> +#endif
>  
> -	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 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");
> +#define GENFSCON(fstype, prefix)			     \
> +	fprintf(fout, "genfscon %s %s " OBJUSERROLETYPE "%s\n", \
> +		fstype, prefix, mls ? ":" SYSTEMLOW : "")
>  
> -	fprintf(fout, "genfscon proc / user_u:base_r:base_t\n");
> +	/*
> +	 * Filesystems whose inodes are labeled from path prefix match
> +	 * relative to the filesystem root.  Depending on the filesystem,
> +	 * only a single label for all inodes may be supported.  Here
> +	 * we list the filesystem types for which per-file labeling is
> +	 * supported using genfscon; any other filesystem type can also
> +	 * be added by only with a single entry for all of its inodes.
> +	 */
> +#ifdef CONFIG_PROC_FS
> +	GENFSCON("proc", "/");
> +#endif
> +#ifdef CONFIG_SECURITY_SELINUX
> +	GENFSCON("selinuxfs", "/");
> +#endif
> +#ifdef CONFIG_SYSFS
> +	GENFSCON("sysfs", "/");
> +#endif
> +#ifdef CONFIG_DEBUG_FS
> +	GENFSCON("debugfs", "/");
> +#endif
> +#ifdef CONFIG_TRACING
> +	GENFSCON("tracefs", "/");
> +#endif
> +#ifdef CONFIG_PSTORE
> +	GENFSCON("pstore", "/");
> +#endif
> +	GENFSCON("cgroup", "/");
> +	GENFSCON("cgroup2", "/");
>  
>  	fclose(fout);
>  
> @@ -144,8 +258,8 @@ int main(int argc, char *argv[])
>  		printf("Wrote policy, but cannot open %s for writing\n", ctxout);
>  		usage(argv[0]);
>  	}
> -	fprintf(fout, "/ user_u:base_r:base_t\n");
> -	fprintf(fout, "/.* user_u:base_r:base_t\n");
> +	fprintf(fout, "/ " OBJUSERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
> +	fprintf(fout, "/.* " OBJUSERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
>  	fclose(fout);
>  
>  	return 0;
> -- 
> 2.20.1
> 

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Dominick Grift