[PATCH v3] scripts/selinux: add basic mls support to mdp

[Stephen Smalley <sds@tycho.nsa.gov>]

Add basic MLS policy support to mdp.  Declares
two sensitivities and two categories, defines
mls constraints for all permissions requiring
dominance (ala MCS), assigns the system-high
level to initial SID contexts and the default user
level, and assigns system-low level to filesystems.

Also reworks the fs_use and genfscon rules to only
generate rules for filesystems that are configured
in the kernel.  In some cases this depends on a specific
config option for security xattrs, in other cases security
xattrs are unconditionally supported by a given filesystem
if the filesystem is enabled, and in some cases the filesystem
is always enabled in the kernel.  Dropped obsolete pseudo
filesystems.

NB The list of fs_use_* and genfscon rules emitted by mdp
is very incomplete compared to refpolicy or Android sepolicy.
We should probably expand it.

Usage:
scripts/selinux/mdp/mdp -m policy.conf file_contexts
checkpolicy -M -o policy policy.conf

Then install the resulting policy and file_contexts as usual.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
---
v3 fixes up the file contexts generation code to also use SYSTEMLOW and
collapse down to a single fprintf call per line.
 scripts/selinux/mdp/mdp.c | 131 ++++++++++++++++++++++++++++++--------
 1 file changed, 103 insertions(+), 28 deletions(-)

diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
index 073fe7537f6c..4223e2fea441 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 +130,87 @@ 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", SYSTEMHIGH,
+			SYSTEMLOW, SYSTEMHIGH);
+	fprintf(fout, ";\n");
+
+#define USERROLETYPE "user_u:base_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 " USERROLETYPE "%s\n",
+			initial_sid_to_string[i], mls ? ":" SYSTEMHIGH : "");
 	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");
-
-	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");
-
-	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");
-
-	fprintf(fout, "genfscon proc / user_u:base_r:base_t\n");
+#define FS_USE(behavior, fstype)			    \
+	fprintf(fout, "fs_use_%s %s " USERROLETYPE "%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
+
+	/*
+	 * Filesystems whose inodes are labeled from allocating task.
+	 */
+	FS_USE("task", "pipefs");
+	FS_USE("task", "sockfs");
+#ifdef CONFIG_POSIX_MQUEUE
+	FS_USE("task", "mqueue");
+#endif
+
+	/*
+	 * 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
+
+
+#define GENFSCON(fstype, prefix)			     \
+	fprintf(fout, "genfscon %s %s " USERROLETYPE "%s\n", \
+		fstype, prefix, mls ? ":" SYSTEMLOW : "")
+
+	/*
+	 * 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.
+	 */
+	GENFSCON("proc", "/");
+	GENFSCON("selinuxfs", "/");
 
 	fclose(fout);
 
@@ -144,8 +219,8 @@ 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, "/ " USERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
+	fprintf(fout, "/.* " USERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
 	fclose(fout);
 
 	return 0;
-- 
2.20.1