librpc/rpc: add dcerpc_sec_verification_trailer_check()

Signed-off-by: Gregor Beck <gbeck@sernet.de>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>

librpc/rpc/dcerpc_util.c

@@ -27,6 +27,7 @@
 #include "librpc/rpc/dcerpc.h"
 #include "librpc/gen_ndr/ndr_dcerpc.h"
 #include "rpc_common.h"
+#include "lib/util/bitmap.h"
 
 /* we need to be able to get/set the fragment length without doing a full
    decode */
@@ -449,3 +450,138 @@ bool dcerpc_sec_vt_header2_equal(const struct dcerpc_sec_vt_header2 *v1,
 
 	return true;
 }
+
+static bool dcerpc_sec_vt_is_valid(const struct dcerpc_sec_verification_trailer *r)
+{
+	bool ret = false;
+	TALLOC_CTX *frame = talloc_stackframe();
+	struct bitmap *commands_seen;
+	int i;
+
+	if (r->count.count == 0) {
+		ret = true;
+		goto done;
+	}
+
+	if (memcmp(r->magic, DCERPC_SEC_VT_MAGIC, sizeof(r->magic)) != 0) {
+		goto done;
+	}
+
+	commands_seen = bitmap_talloc(frame, DCERPC_SEC_VT_COMMAND_ENUM + 1);
+	if (commands_seen == NULL) {
+		goto done;
+	}
+
+	for (i=0; i < r->count.count; i++) {
+		enum dcerpc_sec_vt_command_enum cmd =
+			r->commands[i].command & DCERPC_SEC_VT_COMMAND_ENUM;
+
+		if (bitmap_query(commands_seen, cmd)) {
+			/* Each command must appear at most once. */
+			goto done;
+		}
+		bitmap_set(commands_seen, cmd);
+
+		switch (cmd) {
+		case DCERPC_SEC_VT_COMMAND_BITMASK1:
+		case DCERPC_SEC_VT_COMMAND_PCONTEXT:
+		case DCERPC_SEC_VT_COMMAND_HEADER2:
+			break;
+		default:
+			if ((r->commands[i].u._unknown.length % 4) != 0) {
+				goto done;
+			}
+			break;
+		}
+	}
+	ret = true;
+done:
+	TALLOC_FREE(frame);
+	return ret;
+}
+
+#define CHECK(msg, ok)						\
+do {								\
+	if (!ok) {						\
+		DEBUG(10, ("SEC_VT check %s failed\n", msg));	\
+		return false;					\
+	}							\
+} while(0)
+
+#define CHECK_SYNTAX(msg, s1, s2)					\
+do {								\
+	if (!ndr_syntax_id_equal(&s1, &s2)) {				\
+		TALLOC_CTX *frame = talloc_stackframe();		\
+		DEBUG(10, ("SEC_VT check %s failed: %s vs. %s\n", msg,	\
+			   ndr_syntax_id_to_string(frame, &s1),		\
+			   ndr_syntax_id_to_string(frame, &s1)));	\
+		TALLOC_FREE(frame);					\
+		return false;						\
+	}								\
+} while(0)
+
+
+bool dcerpc_sec_verification_trailer_check(
+		const struct dcerpc_sec_verification_trailer *vt,
+		const uint32_t *bitmask1,
+		const struct dcerpc_sec_vt_pcontext *pcontext,
+		const struct dcerpc_sec_vt_header2 *header2)
+{
+	size_t i;
+
+	if (!dcerpc_sec_vt_is_valid(vt)) {
+		return false;
+	}
+
+	for (i=0; i < vt->count.count; i++) {
+		struct dcerpc_sec_vt *c = &vt->commands[i];
+
+		switch (c->command & DCERPC_SEC_VT_COMMAND_ENUM) {
+		case DCERPC_SEC_VT_COMMAND_BITMASK1:
+			if (bitmask1 == NULL) {
+				CHECK("Bitmask1 must_process_command",
+				      !(c->command & DCERPC_SEC_VT_MUST_PROCESS));
+				break;
+			}
+
+			if (c->u.bitmask1 & DCERPC_SEC_VT_CLIENT_SUPPORTS_HEADER_SIGNING) {
+				CHECK("Bitmask1 client_header_signing",
+				      *bitmask1 & DCERPC_SEC_VT_CLIENT_SUPPORTS_HEADER_SIGNING);
+			}
+			break;
+
+		case DCERPC_SEC_VT_COMMAND_PCONTEXT:
+			if (pcontext == NULL) {
+				CHECK("Pcontext must_process_command",
+				      !(c->command & DCERPC_SEC_VT_MUST_PROCESS));
+				break;
+			}
+
+			CHECK_SYNTAX("Pcontect abstract_syntax",
+				     pcontext->abstract_syntax,
+				     c->u.pcontext.abstract_syntax);
+			CHECK_SYNTAX("Pcontext transfer_syntax",
+				     pcontext->transfer_syntax,
+				     c->u.pcontext.transfer_syntax);
+			break;
+
+		case DCERPC_SEC_VT_COMMAND_HEADER2: {
+			if (header2 == NULL) {
+				CHECK("Header2 must_process_command",
+				      !(c->command & DCERPC_SEC_VT_MUST_PROCESS));
+				break;
+			}
+
+			CHECK("Header2", dcerpc_sec_vt_header2_equal(header2, &c->u.header2));
+			break;
+		}
+
+		default:
+			CHECK("Unknown must_process_command",
+			      !(c->command & DCERPC_SEC_VT_MUST_PROCESS));
+			break;
+		}
+	}
+
+	return true;
+}

librpc/rpc/rpc_common.h

@@ -338,4 +338,22 @@ struct dcerpc_sec_vt_header2 dcerpc_sec_vt_header2_from_ncacn_packet(const struc
 bool dcerpc_sec_vt_header2_equal(const struct dcerpc_sec_vt_header2 *v1,
 				 const struct dcerpc_sec_vt_header2 *v2);
 
+/**
+ * Check for consistency of the security verification trailer with the PDU header.
+ * See <a href="http://msdn.microsoft.com/en-us/library/cc243559.aspx">MS-RPCE 2.2.2.13</a>.
+ * A check with an empty trailer succeeds.
+ *
+ * @param[in] vt a pointer to the security verification trailer.
+ * @param[in] bitmask1 which flags were negotiated on the connection.
+ * @param[in] pcontext the syntaxes negotiatied for the presentation context.
+ * @param[in] header2 some fields from the PDU header.
+ *
+ * @retval true on success.
+ */
+bool dcerpc_sec_verification_trailer_check(
+		const struct dcerpc_sec_verification_trailer *vt,
+		const uint32_t *bitmask1,
+		const struct dcerpc_sec_vt_pcontext *pcontext,
+		const struct dcerpc_sec_vt_header2 *header2);
+
 #endif /* __DEFAULT_LIBRPC_RPCCOMMON_H__ */