RFE: policydb read validation

security/selinux/include/limits.h

@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Limits for various policy database elements.
+ */
+
+/*
+ * Maximum supported depth of conditional expressions.
+ */
+#define COND_EXPR_MAXDEPTH 10
+
+/*
+ * Maximum supported depth for constraint expressions.
+ */
+#define CEXPR_MAXDEPTH 5
+
+/*
+ * Maximum supported identifier value.
+ *
+ * Reasoning: The most used symbols are types and they need to fit into
+ *            an u16 for the avtab entries. Keep U16_MAX as special value
+ *            and U16_MAX-1 to avoid accidental overflows into U16_MAX.
+ */
+#define IDENTIFIER_MAXVALUE (U16_MAX - 2)
+
+/*
+ * Maximum supported length of security context strings.
+ *
+ * Reasoning: The string must fir into a PAGE_SIZE.
+ */
+#define CONTEXT_MAXLENGTH 4000
+
+/*
+ * Maximum supported boolean name length.
+ */
+#define BOOLEAN_NAME_MAXLENGTH 64
+
+/*
+ * Maximum supported security class and common class name length.
+ */
+#define CLASS_NAME_MAXLENGTH 64
+
+/*
+ * Maximum supported permission name length.
+ */
+#define PERMISSION_NAME_MAXLENGTH 64
+
+/*
+ * Maximum supported user name length.
+ */
+#define USER_NAME_MAXLENGTH 64
+
+/*
+ * Maximum supported role name length.
+ */
+#define ROLE_NAME_MAXLENGTH 64
+
+/*
+ * Maximum supported type name length.
+ */
+#define TYPE_NAME_MAXLENGTH 1024
+
+/*
+ * Maximum supported sensitivity name length.
+ */
+#define SENSITIVITY_NAME_MAXLENGTH 32
+
+/*
+ * Maximum supported category name length.
+ */
+#define CATEGORY_NAME_MAXLENGTH 16
+
+/*
+ * Maximum supported path name length for keys in filename transitions.
+ */
+#define FILETRANSKEY_NAME_MAXLENGTH 1024
+
+/*
+ * Maximum supported filesystem name length.
+ */
+#define FILESYSTEM_NAME_MAXLENGTH 128
+
+/*
+ * Maximum supported path prefix length for genfs statements.
+ */
+#define GENFS_PATH_MAXLENGTH 1024
+
+/*
+ * Maximum supported Infiniband device name length.
+ */
+#define INFINIBAND_DEVNAME_MAXLENGTH 256

security/selinux/include/security.h

@@ -224,6 +224,7 @@ int security_read_policy(void **data, size_t *len);
 int security_read_state_kernel(void **data, size_t *len);
 int security_policycap_supported(unsigned int req_cap);
 
+/* Maximum supported number of permissions per class */
 #define SEL_VEC_MAX 32
 struct av_decision {
 	u32 allowed;

security/selinux/ss/avtab.c

@@ -349,7 +349,7 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 	struct avtab_extended_perms xperms;
 	__le32 buf32[ARRAY_SIZE(xperms.perms.p)];
 	int rc;
-	unsigned int set, vers = pol->policyvers;
+	unsigned int vers = pol->policyvers;
 
 	memset(&key, 0, sizeof(struct avtab_key));
 	memset(&datum, 0, sizeof(struct avtab_datum));
@@ -360,9 +360,12 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 			pr_err("SELinux: avtab: truncated entry\n");
 			return rc;
 		}
+		/* Read five or more items: source type, target type,
+		 * target class, AV type, and at least one datum.
+		 */
 		items2 = le32_to_cpu(buf32[0]);
-		if (items2 > ARRAY_SIZE(buf32)) {
-			pr_err("SELinux: avtab: entry overflow\n");
+		if (items2 < 5 || items2 > ARRAY_SIZE(buf32)) {
+			pr_err("SELinux: avtab: invalid item count\n");
 			return -EINVAL;
 		}
 		rc = next_entry(buf32, fp, sizeof(u32) * items2);
@@ -391,6 +394,13 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 			return -EINVAL;
 		}
 
+		if (!policydb_type_isvalid(pol, key.source_type) ||
+		    !policydb_type_isvalid(pol, key.target_type) ||
+		    !policydb_class_isvalid(pol, key.target_class)) {
+			pr_err("SELinux: avtab: invalid type or class\n");
+			return -EINVAL;
+		}
+
 		val = le32_to_cpu(buf32[items++]);
 		enabled = (val & AVTAB_ENABLED_OLD) ? AVTAB_ENABLED : 0;
 
@@ -409,8 +419,20 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 
 		for (i = 0; i < ARRAY_SIZE(spec_order); i++) {
 			if (val & spec_order[i]) {
+				if (items >= items2) {
+					pr_err("SELinux: avtab: entry has too many items (%d/%d)\n",
+					       items + 1, items2);
+					return -EINVAL;
+				}
 				key.specified = spec_order[i] | enabled;
 				datum.u.data = le32_to_cpu(buf32[items++]);
+
+				if ((key.specified & AVTAB_TYPE) &&
+				    !policydb_simpletype_isvalid(pol, datum.u.data)) {
+					pr_err("SELinux: avtab: invalid type\n");
+					return -EINVAL;
+				}
+
 				rc = insertf(a, &key, &datum, p);
 				if (rc)
 					return rc;
@@ -444,9 +466,13 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 		return -EINVAL;
 	}
 
-	set = hweight16(key.specified & (AVTAB_XPERMS | AVTAB_TYPE | AVTAB_AV));
-	if (!set || set > 1) {
-		pr_err("SELinux:  avtab:  more than one specifier\n");
+	if (hweight16(key.specified & ~AVTAB_ENABLED) != 1) {
+		pr_err("SELinux:  avtab:  not exactly one specifier\n");
+		return -EINVAL;
+	}
+
+	if (key.specified & ~AVTAB_SPECIFIER_MASK) {
+		pr_err("SELinux:  avtab:  invalid specifier\n");
 		return -EINVAL;
 	}
 
@@ -471,6 +497,10 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 			pr_err("SELinux: avtab: truncated entry\n");
 			return rc;
 		}
+		if (!avtab_is_valid_xperm_specified(xperms.specified))
+			pr_warn_once_policyload(pol,
+						"SELinux: avtab: unsupported xperm specifier %#x\n",
+						xperms.specified);
 		rc = next_entry(&xperms.driver, fp, sizeof(u8));
 		if (rc) {
 			pr_err("SELinux: avtab: truncated entry\n");
@@ -494,7 +524,7 @@ int avtab_read_item(struct avtab *a, struct policy_file *fp, struct policydb *po
 		datum.u.data = le32_to_cpu(*buf32);
 	}
 	if ((key.specified & AVTAB_TYPE) &&
-	    !policydb_type_isvalid(pol, datum.u.data)) {
+	    !policydb_simpletype_isvalid(pol, datum.u.data)) {
 		pr_err("SELinux: avtab: invalid type\n");
 		return -EINVAL;
 	}
@@ -525,6 +555,11 @@ int avtab_read(struct avtab *a, struct policy_file *fp, struct policydb *pol)
 		goto bad;
 	}
 
+	/* avtab_read_item() reads at least 96 bytes for any valid entry */
+	rc = size_check(3 * sizeof(u32), nel, fp);
+	if (rc)
+		goto bad;
+
 	rc = avtab_alloc(a, nel);
 	if (rc)
 		goto bad;

security/selinux/ss/avtab.h

@@ -44,6 +44,7 @@ struct avtab_key {
 	 AVTAB_XPERMS_DONTAUDIT)
 #define AVTAB_ENABLED_OLD 0x80000000 /* reserved for used in cond_avtab */
 #define AVTAB_ENABLED	  0x8000 /* reserved for used in cond_avtab */
+#define AVTAB_SPECIFIER_MASK (AVTAB_AV | AVTAB_TYPE | AVTAB_XPERMS | AVTAB_ENABLED)
 	u16 specified; /* what field is specified */
 };
 
@@ -68,6 +69,18 @@ struct avtab_extended_perms {
 	struct extended_perms_data perms;
 };
 
+static inline bool avtab_is_valid_xperm_specified(u8 specified)
+{
+	switch (specified) {
+	case AVTAB_XPERMS_IOCTLFUNCTION:
+	case AVTAB_XPERMS_IOCTLDRIVER:
+	case AVTAB_XPERMS_NLMSG:
+		return true;
+	default:
+		return false;
+	}
+}
+
 struct avtab_datum {
 	union {
 		u32 data; /* access vector or type value */