Support Android/M and official v30 sepolicy format

Some Android M devices use a slightly different format for the sepolicy
file.  Compatibility for this is not present in SELinuxProject/selinux
master.  Google does provide a patch for the kernel itself to be able to
handle both formats - https://android-review.googlesource.com/#/c/179568/ -
but not for libsepol. This patch is a port of the kernel patch to
libsepol.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

libsepol/src/android_m_compat.c

@@ -0,0 +1,13 @@
+#include <stdio.h>
+
+#include "android_m_compat.h"
+
+unsigned int avtab_android_m_compat;
+
+void avtab_android_m_compat_set(void)
+{
+	if (!avtab_android_m_compat) {
+		fprintf(stderr, "(Android M policy compatibility mode)\n");
+		avtab_android_m_compat = 1;
+	}
+}

libsepol/src/android_m_compat.h

@@ -0,0 +1,18 @@
+/*
+ * extended permissions compatibility. Make ToT Android kernels compatible
+ * with Android M releases
+ */
+#define AVTAB_OPTYPE_ALLOWED	0x1000
+#define AVTAB_OPTYPE_AUDITALLOW	0x2000
+#define AVTAB_OPTYPE_DONTAUDIT	0x4000
+#define AVTAB_OPTYPE		(AVTAB_OPTYPE_ALLOWED | \
+				AVTAB_OPTYPE_AUDITALLOW | \
+				AVTAB_OPTYPE_DONTAUDIT)
+#define AVTAB_XPERMS_OPTYPE	4
+
+#define avtab_xperms_to_optype(x) (x << AVTAB_XPERMS_OPTYPE)
+#define avtab_optype_to_xperms(x) (x >> AVTAB_XPERMS_OPTYPE)
+
+extern unsigned int avtab_android_m_compat;
+
+void avtab_android_m_compat_set(void);

libsepol/src/avtab.c

@@ -48,6 +48,7 @@
 
 #include "debug.h"
 #include "private.h"
+#include "android_m_compat.h"
 
 /* Based on MurmurHash3, written by Austin Appleby and placed in the
  * public domain.
@@ -440,6 +441,7 @@ int avtab_read_item(struct policy_file *fp, uint32_t vers, avtab_t * a,
 	avtab_key_t key;
 	avtab_datum_t datum;
 	avtab_extended_perms_t xperms;
+	unsigned int android_m_compat_optype = 0;
 	unsigned set;
 	unsigned int i;
 	int rc;
@@ -529,6 +531,13 @@ int avtab_read_item(struct policy_file *fp, uint32_t vers, avtab_t * a,
 	key.target_class = le16_to_cpu(buf16[items++]);
 	key.specified = le16_to_cpu(buf16[items++]);
 
+	if ((key.specified & AVTAB_OPTYPE) &&
+			(vers == POLICYDB_VERSION_XPERMS_IOCTL)) {
+		key.specified = avtab_optype_to_xperms(key.specified);
+		android_m_compat_optype = 1;
+		avtab_android_m_compat_set();
+	}
+
 	set = 0;
 	for (i = 0; i < ARRAY_SIZE(spec_order); i++) {
 		if (key.specified & spec_order[i])
@@ -551,12 +560,24 @@ int avtab_read_item(struct policy_file *fp, uint32_t vers, avtab_t * a,
 			return -1;
 		}
 		xperms.specified = buf8;
-		rc = next_entry(&buf8, fp, sizeof(uint8_t));
-		if (rc < 0) {
-			ERR(fp->handle, "truncated entry");
-			return -1;
+		if (avtab_android_m_compat ||
+				((xperms.specified != AVTAB_XPERMS_IOCTLFUNCTION) &&
+				(xperms.specified != AVTAB_XPERMS_IOCTLDRIVER) &&
+				(vers == POLICYDB_VERSION_XPERMS_IOCTL))) {
+			xperms.driver = xperms.specified;
+			if (android_m_compat_optype)
+				xperms.specified = AVTAB_XPERMS_IOCTLDRIVER;
+			else
+				xperms.specified = AVTAB_XPERMS_IOCTLFUNCTION;
+			avtab_android_m_compat_set();
+		} else {
+			rc = next_entry(&buf8, fp, sizeof(uint8_t));
+			if (rc < 0) {
+				ERR(fp->handle, "truncated entry");
+				return -1;
+			}
+			xperms.driver = buf8;
 		}
-		xperms.driver = buf8;
 		rc = next_entry(buf32, fp, sizeof(uint32_t)*8);
 		if (rc < 0) {
 			ERR(fp->handle, "truncated entry");

libsepol/src/write.c

@@ -44,6 +44,7 @@
 #include "debug.h"
 #include "private.h"
 #include "mls.h"
+#include "android_m_compat.h"
 
 struct policy_data {
 	struct policy_file *fp;
@@ -217,7 +218,11 @@ static int avtab_write_item(policydb_t * p,
 	buf16[0] = cpu_to_le16(cur->key.source_type);
 	buf16[1] = cpu_to_le16(cur->key.target_type);
 	buf16[2] = cpu_to_le16(cur->key.target_class);
-	buf16[3] = cpu_to_le16(cur->key.specified);
+	if (avtab_android_m_compat && (cur->key.specified & AVTAB_XPERMS) &&
+		    (cur->datum.xperms->specified == AVTAB_XPERMS_IOCTLDRIVER))
+		buf16[3] = cpu_to_le16(avtab_xperms_to_optype(cur->key.specified));
+	else
+		buf16[3] = cpu_to_le16(cur->key.specified);
 	items = put_entry(buf16, sizeof(uint16_t), 4, fp);
 	if (items != 4)
 		return POLICYDB_ERROR;
@@ -237,10 +242,12 @@ static int avtab_write_item(policydb_t * p,
 	}
 
 	if (cur->key.specified & AVTAB_XPERMS) {
-		buf8 = cur->datum.xperms->specified;
-		items = put_entry(&buf8, sizeof(uint8_t),1,fp);
-		if (items != 1)
-			return POLICYDB_ERROR;
+		if (avtab_android_m_compat == 0) {
+			buf8 = cur->datum.xperms->specified;
+			items = put_entry(&buf8, sizeof(uint8_t),1,fp);
+			if (items != 1)
+				return POLICYDB_ERROR;
+		}
 		buf8 = cur->datum.xperms->driver;
 		items = put_entry(&buf8, sizeof(uint8_t),1,fp);
 		if (items != 1)