libdhcp: Reduce stack usage

1 files changed, 157 insertions, 117 deletions

diff --git a/libdhcp/dhcp_client.c b/libdhcp/dhcp_client.c
index 3c6ed8d..bb21564 100644
--- a/libdhcp/dhcp_client.c
+++ b/libdhcp/dhcp_client.c
@@ -172,6 +172,71 @@ struct dhcp_client {
 };
 
 /**
+ * For convenience in switch blocks, a list of the states that, when
+ * msgtyp==DHCP_MSGTYP_REQUEST, dhcp_client_send() has assert()ed the state is
+ * not.
+ */
+#define IMPOSSIBLE_REQUEST_STATES \
+		     STATE_INIT: \
+		case STATE_REQUESTING: \
+		case STATE_REBINDING: \
+		case STATE_REBOOTING
+
+static inline enum requirement dhcp_table5(typeof((struct dhcp_client){}.state) state,
+                               uint8_t msgtyp,
+                               uint8_t opt) {
+	/* Encode "Table 5: Fields and options used by DHCP clients"
+	 * from
+	 * https://datatracker.ietf.org/doc/html/rfc2131#page-38.  */
+#define INC_ADDR ({	  \
+			enum requirement req; \
+			switch (state) { \
+			case STATE_SELECTING: case STATE_INIT_REBOOT: req = MUST;     break; \
+			case STATE_BOUND: case STATE_RENEWING:        req = MUST_NOT; break; \
+			case IMPOSSIBLE_REQUEST_STATES: default:      req = _SHOULD_NOT_HAPPEN; \
+			} \
+			req; \
+		})
+#define INC_SERVER ({	  \
+			enum requirement req; \
+			switch (state) { \
+			case STATE_SELECTING:                                          req = MUST;     break; \
+			case STATE_INIT_REBOOT: case STATE_BOUND: case STATE_RENEWING: req = MUST_NOT; break; \
+			case IMPOSSIBLE_REQUEST_STATES: default:                       req = _SHOULD_NOT_HAPPEN; \
+			} \
+			req; \
+		})
+	struct { enum requirement cols[5]; } row;
+#define ROW(...) row = (typeof(row)){{ __VA_ARGS__ }}
+	switch (opt) {
+	/* Option                            DISCOVER    INFORM      REQUEST     DECLINE   RELEASE  */
+	/* ------                            ----------  ----------  ----------  --------  -------- */
+	case DHCP_OPT_ADDRESS_REQUEST:   ROW(MAY,        MUST_NOT,   INC_ADDR,   MUST,     MUST_NOT); break;
+	case DHCP_OPT_ADDRESS_TIME:      ROW(MAY,        MUST_NOT,   MAY,        MUST_NOT, MUST_NOT); break;
+	case DHCP_OPT_OVERLOAD:          ROW(MAY,        MAY,        MAY,        MAY,      MAY     ); break;
+	case DHCP_OPT_DHCP_MSG_TYPE:     ROW(MUST,       MUST,       MUST,       MUST,     MUST    ); break;
+	case DHCP_OPT_CLIENT_ID:         ROW(MAY,        MAY,        MAY,        MAY,      MAY     ); break;
+	case DHCP_OPT_CLASS_ID:          ROW(MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT); break;
+	case DHCP_OPT_DHCP_SERVER_ID:    ROW(MUST_NOT,   MUST_NOT,   INC_SERVER, MUST,     MUST    ); break;
+	case DHCP_OPT_PARAMETER_LIST:    ROW(MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT); break;
+	case DHCP_OPT_DHCP_MAX_MSG_SIZE: ROW(MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT); break;
+	case DHCP_OPT_DHCP_MESSAGE:      ROW(SHOULD_NOT, SHOULD_NOT, SHOULD_NOT, SHOULD,   SHOULD  ); break;
+	default:                         ROW(MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT);
+	}
+#undef ROW
+#undef INC_SERVER
+#undef INC_ADDR
+	switch (msgtyp) {
+	case DHCP_MSGTYP_DISCOVER: return row.cols[0];
+	case DHCP_MSGTYP_INFORM:   return row.cols[1];
+	case DHCP_MSGTYP_REQUEST:  return row.cols[2];
+	case DHCP_MSGTYP_DECLINE:  return row.cols[3];
+	case DHCP_MSGTYP_RELEASE:  return row.cols[4];
+	default:                   return _SHOULD_NOT_HAPPEN;
+	}
+}
+
+/**
  * @param client->state
  * @param client->self_eth_addr
  * @param client->xid
@@ -200,14 +265,6 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 		       client->state == STATE_BOUND       || /* T1 expired, start renew */
 		       client->state == STATE_RENEWING    ); /* T2 expired, start rebind */
 
-	/* For convenience in switch blocks, a list of the states that
-	 * are not in the above assert().  */
-#define IMPOSSIBLE_REQUEST_STATES \
-		     STATE_INIT: \
-		case STATE_REQUESTING: \
-		case STATE_REBINDING: \
-		case STATE_REBOOTING
-
 	/**********************************************************************\
 	 * Setup                                                              *
 	\**********************************************************************/
@@ -315,94 +372,74 @@ static bool dhcp_client_send(struct dhcp_client *client, uint8_t msgtyp, const c
 	msg.options[optlen++] = dhcp_magic_cookie[2];
 	msg.options[optlen++] = dhcp_magic_cookie[3];
 
-	/* Options.
-	 * https://datatracker.ietf.org/doc/html/rfc2131#page-38 */
-	static uint8_t parameter_request_list[] = {
-		DHCP_OPT_SUBNET_MASK,
-		DHCP_OPT_ROUTER,
-		DHCP_OPT_RENEWAL_TIME,
-		DHCP_OPT_REBINDING_TIME,
-	};
-	const struct {
-		bool                    have_cols;
-		enum requirement        cols[5];
-		size_t                  val_len;
-		const void             *val_ptr;
-	} options[0x100] = {
-#define V(x) sizeof(x), &(x)
-#define NONE 0, NULL
-		/* Encode the table from
-		 * https://datatracker.ietf.org/doc/html/rfc2131#page-38 */
-#define INC_ADDR ({                                                                             \
-			enum requirement req;                                                   \
-			switch (client->state) {                                                \
-			case STATE_SELECTING: case STATE_INIT_REBOOT: req = MUST;     break;    \
-			case STATE_BOUND: case STATE_RENEWING:        req = MUST_NOT; break;    \
-			case IMPOSSIBLE_REQUEST_STATES: default:      req = _SHOULD_NOT_HAPPEN; \
-			}                                                                       \
-			req;                                                                    \
-		})
-#define INC_SERVER ({                                                                                            \
-			enum requirement req;                                                                    \
-			switch (client->state) {                                                                 \
-			case STATE_SELECTING:                                          req = MUST;     break;    \
-			case STATE_INIT_REBOOT: case STATE_BOUND: case STATE_RENEWING: req = MUST_NOT; break;    \
-			case IMPOSSIBLE_REQUEST_STATES: default:                       req = _SHOULD_NOT_HAPPEN; \
-			}                                                                                        \
-			req;                                                                                     \
-		})
-		/* Option                             DISCOVER    INFORM      REQUEST     DECLINE   RELEASE */
-		/* ------                             ----------  ----------  ----------  --------  -------- */
-		[DHCP_OPT_ADDRESS_REQUEST]   = { 1, { MAY,        MUST_NOT,   INC_ADDR,   MUST,     MUST_NOT }, V(client->lease_client_addr) },
-		[DHCP_OPT_ADDRESS_TIME]      = { 1, { MAY,        MUST_NOT,   MAY,        MUST_NOT, MUST_NOT }, NONE },
-		[DHCP_OPT_OVERLOAD]          = { 1, { MAY,        MAY,        MAY,        MAY,      MAY      }, NONE },
-		[DHCP_OPT_DHCP_MSG_TYPE]     = { 1, { MUST,       MUST,       MUST,       MUST,     MUST     }, V(msgtyp) },
-		[DHCP_OPT_CLIENT_ID]         = { 1, { MAY,        MAY,        MAY,        MAY,      MAY      }, client->self_id_len, client->self_id_dat },
-		[DHCP_OPT_CLASS_ID]          = { 1, { MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT }, NONE },
-		[DHCP_OPT_DHCP_SERVER_ID]    = { 1, { MUST_NOT,   MUST_NOT,   INC_SERVER, MUST,     MUST     }, V(client->lease_server_id) },
-		[DHCP_OPT_PARAMETER_LIST]    = { 1, { MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT }, V(parameter_request_list) },
-		[DHCP_OPT_DHCP_MAX_MSG_SIZE] = { 1, { MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT },
-		                                 CONFIG_DHCP_OPT_SIZE > DHCP_MSG_MIN_MAX_OPT_SIZE ? 2 : 0,
-		                                 CONFIG_DHCP_OPT_SIZE > DHCP_MSG_MIN_MAX_OPT_SIZE ? &(struct{uint16be_t;}){uint16be_marshal(/*IP*/20+/*UDP*/8+sizeof(msg))} : NULL },
-		[DHCP_OPT_DHCP_MESSAGE]      = { 1, { SHOULD_NOT, SHOULD_NOT, SHOULD_NOT, SHOULD,   SHOULD   }, errstr ? strlen(errstr) : 0, errstr },
-		[0]/* All others */          = { 0, { MAY,        MAY,        MAY,        MUST_NOT, MUST_NOT }, NONE },
-
-		[DHCP_OPT_HOSTNAME]          = { 0, {0},
-		                                 strnlen(client->self_hostname, sizeof(client->self_hostname)),
-		                                 client->self_hostname },
-	};
-	int col;
-	switch (msgtyp) {
-	case DHCP_MSGTYP_DISCOVER: col = 0; break;
-	case DHCP_MSGTYP_INFORM:   col = 1; break;
-	case DHCP_MSGTYP_REQUEST:  col = 2; break;
-	case DHCP_MSGTYP_DECLINE:  col = 3; break;
-	case DHCP_MSGTYP_RELEASE:  col = 4; break;
-	default: assert_notreached("invalid message type for client to send");
-	}
+	/* Options.  */
 	for (uint8_t opt = 1; opt < 255; opt++) {
-		enum requirement req = options[opt].have_cols
-			? options[opt].cols[col]
-			: options[0].cols[col];
+		enum requirement req = dhcp_table5(client->state, msgtyp, opt);
 		switch (req) {
 		case MUST_NOT:
 			/* Do nothing.  */
 			break;
 		case MUST:
-			assert(options[opt].val_len);
-			/* fall-through */
 		case SHOULD:
 		case SHOULD_NOT:
 		case MAY:
-			if (options[opt].val_len) {
-				assert(options[opt].val_len <= UINT16_MAX);
-				for (size_t done = 0; done < options[opt].val_len;) {
-					uint8_t len = options[opt].val_len - done > UINT8_MAX
+			struct { size_t len; const void *ptr; } val;
+			uint8_t _val_prl[] = {
+				DHCP_OPT_SUBNET_MASK,
+				DHCP_OPT_ROUTER,
+				DHCP_OPT_RENEWAL_TIME,
+				DHCP_OPT_REBINDING_TIME,
+			};
+			uint16be_t _val16 ;
+#define V_RAW(len, ptr) val = (typeof(val)){ len, ptr }
+#define V_OBJ(x)        V_RAW(sizeof(x), &x)
+#define V_STR(x)        V_RAW(x ? strlen(x) : 0, x)
+#define V_STRN(x)       V_RAW(strnlen(x, sizeof(x)), x)
+#define V_NONE()        V_RAW(0, NULL)
+			switch (opt) {
+			/* For clarity, list all options mentioned in "Table 5:
+			 * Fields and options used by DHCP clients" from
+			 * https://datatracker.ietf.org/doc/html/rfc2131#page-38,
+			 * even if we don't have a value for them.  */
+			case DHCP_OPT_ADDRESS_REQUEST:    V_OBJ(client->lease_client_addr); break;
+			case DHCP_OPT_ADDRESS_TIME:       V_NONE(); break;
+			case DHCP_OPT_OVERLOAD:           V_NONE(); break;
+			case DHCP_OPT_DHCP_MSG_TYPE:      V_OBJ(msgtyp); break;
+			case DHCP_OPT_CLIENT_ID:          V_RAW(client->self_id_len, client->self_id_dat); break;
+			case DHCP_OPT_CLASS_ID:           V_NONE(); break;
+			case DHCP_OPT_DHCP_SERVER_ID:     V_OBJ(client->lease_server_id); break;
+			case DHCP_OPT_PARAMETER_LIST:     V_OBJ(_val_prl); break;
+			case DHCP_OPT_DHCP_MAX_MSG_SIZE:
+				if (CONFIG_DHCP_OPT_SIZE <= DHCP_MSG_MIN_MAX_OPT_SIZE)
+					V_NONE();
+				else {
+					_val16 = uint16be_marshal(20 /* IP header */ +
+					                          8  /* UDP header */ +
+					                          sizeof(msg));
+					V_OBJ(_val16);
+				}
+				break;
+			case DHCP_OPT_DHCP_MESSAGE:      V_STR(errstr); break;
+			/* "Site-specific" and "All others".  */
+			case DHCP_OPT_HOSTNAME:          V_STRN(client->self_hostname); break;
+			default:                         V_NONE();
+			};
+#undef V_NONE
+#undef V_STRN
+#undef V_STR
+#undef V_OBJ
+#undef V_RAW
+			if (req == MUST)
+				assert(val.len);
+			if (val.len) {
+				assert(val.len <= UINT16_MAX);
+				for (size_t done = 0; done < val.len;) {
+					uint8_t len = val.len - done > UINT8_MAX
 						? UINT8_MAX
-						: options[opt].val_len - done;
+						: val.len - done;
 					msg.options[optlen++] = opt;
 					msg.options[optlen++] = len;
-					memcpy(&msg.options[optlen], &((char*)options[opt].val_ptr)[done], len);
+					memcpy(&msg.options[optlen], &((char*)val.ptr)[done], len);
 					optlen += len;
 					done += len;
 				}
@@ -484,6 +521,38 @@ static inline void _dhcp_client_recv_consolidate_opts(struct dhcp_recv_msg *ret,
 	}
 }
 
+static inline enum requirement dhcp_table3(uint8_t req_msgtyp, uint8_t resp_msgtyp, uint8_t resp_opt) {
+	/* Encode "Table 3: Fields and options used by DHCP servers"
+	 * from https://datatracker.ietf.org/doc/html/rfc2131#page-29,
+	 * with modifications from
+	 * https://datatracker.ietf.org/doc/html/rfc6842#page-4.  */
+	struct { enum requirement cols[3]; } row;
+#define ROW(...) row = (typeof(row)){{ __VA_ARGS__ }}
+	switch (resp_opt) {
+	/*   Option                          DHCPOFFER DHCPACK     DHCPNAK  */
+	/*   --------------------------      --------  ----------  -------- */
+	case DHCP_OPT_ADDRESS_REQUEST:   ROW(MUST_NOT, MUST_NOT,   MUST_NOT); break;
+	case DHCP_OPT_ADDRESS_TIME:      ROW(MUST,     req_msgtyp == DHCP_MSGTYP_REQUEST ? MUST : MUST_NOT,
+	                                                           MUST_NOT); break;
+	case DHCP_OPT_OVERLOAD:          ROW(MAY,      MAY,        MUST_NOT); break;
+	case DHCP_OPT_DHCP_MSG_TYPE:     ROW(MUST,     MUST,       MUST    ); break;
+	case DHCP_OPT_PARAMETER_LIST:    ROW(MUST_NOT, MUST_NOT,   MUST_NOT); break;
+	case DHCP_OPT_DHCP_MESSAGE:      ROW(SHOULD,   SHOULD,     SHOULD  ); break;
+	case DHCP_OPT_CLIENT_ID:         ROW(MAY,      MAY,        MAY     ); /* MUST_NOTs changed to MAY, per RFC 6842 */ break;
+	case DHCP_OPT_CLASS_ID:          ROW(MAY,      MAY,        MAY     ); break;
+	case DHCP_OPT_DHCP_SERVER_ID:    ROW(MUST,     MUST,       MUST    ); break;
+	case DHCP_OPT_DHCP_MAX_MSG_SIZE: ROW(MUST_NOT, MUST_NOT,   MUST_NOT); break;
+	default:                         ROW(MAY,      MAY,        MUST_NOT);
+	}
+#undef ROW
+	switch (resp_msgtyp) {
+	case DHCP_MSGTYP_OFFER: return row.cols[0];
+	case DHCP_MSGTYP_ACK:   return row.cols[1];
+	case DHCP_MSGTYP_NAK:   return row.cols[2];
+	default:                return _SHOULD_NOT_HAPPEN;
+	}
+}
+
 /**
  * @param client->sock
  * @param client->self_eth_addr
@@ -589,41 +658,12 @@ static ssize_t dhcp_client_recv(struct dhcp_client *client, struct dhcp_recv_msg
 	if (optoverload & 2u)
 		_dhcp_client_recv_consolidate_opts(ret, ret->raw.sname, sizeof(ret->raw.sname));
 	/* Validate presence of options.  */
-	const struct {
-		bool                    have_cols;
-		enum requirement        cols[3];
-	} option_req[0x100] = {
-		/* Enocde the table from
-		 * https://datatracker.ietf.org/doc/html/rfc2131#page-29, with modifications from
-		 * https://datatracker.ietf.org/doc/html/rfc6842#page-4 */
-#define REQ_TIME client->last_sent_msgtyp == DHCP_MSGTYP_REQUEST ? MUST : MUST_NOT
-		/* Option                             DHCPOFFER DHCPACK     DHCPNAK */
-		/* ------                             --------  ----------  -------- */
-		[DHCP_OPT_ADDRESS_REQUEST]   = { 1, { MUST_NOT, MUST_NOT,   MUST_NOT } },
-		[DHCP_OPT_ADDRESS_TIME]      = { 1, { MUST,     REQ_TIME,   MUST_NOT } },
-		[DHCP_OPT_OVERLOAD]          = { 1, { MAY,      MAY,        MUST_NOT } },
-		[DHCP_OPT_DHCP_MSG_TYPE]     = { 1, { MUST,     MUST,       MUST     } },
-		[DHCP_OPT_PARAMETER_LIST]    = { 1, { MUST_NOT, MUST_NOT,   MUST_NOT } },
-		[DHCP_OPT_DHCP_MESSAGE]      = { 1, { SHOULD,   SHOULD,     SHOULD   } },
-		[DHCP_OPT_CLIENT_ID]         = { 1, { MAY,      MAY,        MAY      } }, /* MUST_NOTs changed to MAY, per RFC 6842 */
-		[DHCP_OPT_CLASS_ID]          = { 1, { MAY,      MAY,        MAY      } },
-		[DHCP_OPT_DHCP_SERVER_ID]    = { 1, { MUST,     MUST,       MUST     } },
-		[DHCP_OPT_DHCP_MAX_MSG_SIZE] = { 1, { MUST_NOT, MUST_NOT,   MUST_NOT } },
-		[0]/* All others */          = { 0, { MAY,      MAY,        MUST_NOT } },
-	};
 	if (!ret->options[DHCP_OPT_DHCP_MSG_TYPE].len)
 		goto ignore;
-	int col;
-	switch (ret->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0]) {
-	case DHCP_MSGTYP_OFFER: col = 0; break;
-	case DHCP_MSGTYP_ACK:   col = 1; break;
-	case DHCP_MSGTYP_NAK:   col = 2; break;
-	default:                goto ignore;
-	}
 	for (uint8_t opt = 1; opt < 255; opt++) {
-		enum requirement req = option_req[opt].have_cols
-			? option_req[opt].cols[col]
-			: option_req[0].cols[col];
+		enum requirement req = dhcp_table3(client->last_sent_msgtyp,
+		                                   ret->options[DHCP_OPT_DHCP_MSG_TYPE].dat[0],
+		                                   opt);
 		switch (req) {
 		case MUST:
 			if (!ret->options[opt].len)
@@ -639,7 +679,7 @@ static ssize_t dhcp_client_recv(struct dhcp_client *client, struct dhcp_recv_msg
 			/* Do nothing.  */
 			break;
 		case _SHOULD_NOT_HAPPEN:
-			assert_notreached("bad table");
+			goto ignore;
 		}
 	}
 	/* Validate values of options.  */