wip: Build with -Wconversionlukeshu/safe-conversion

I think this found a real bug in the dhcp packet parser.

I don't think anything called lib9p_str{,n}() values that could be big
enough, but their bounds-checking was broken.

1 files changed, 17 insertions, 9 deletions

diff --git a/libhw_cr/w5500.c b/libhw_cr/w5500.c
index e676364..8ec3f4d 100644
--- a/libhw_cr/w5500.c
+++ b/libhw_cr/w5500.c
@@ -68,6 +68,10 @@
  */
 
 #include <inttypes.h> /* for PRIu{n} */
+#include <limits.h>   /* for SSIZE_MAX, not set by newlib */
+#ifndef SSIZE_MAX
+#define SSIZE_MAX (SIZE_MAX >> 1)
+#endif
 
 /* TODO: Write a <libhw/generic/gpio.h> to avoid w5500.c being
  * pico-sdk-specific.  */
@@ -318,14 +322,15 @@ void _w5500_init(struct w5500 *chip,
 #if CONFIG_W5500_VALIDATE_SPI
 	/* Validate that SPI works correctly.  */
 	bool spi_ok = true;
-	for (uint16_t a = 0; a < 0x100; a++) {
+	uint8_t a = 0;
+	do {
 		w5500ll_write_sock_reg(chip->spidev, 0, mode, a);
 		uint8_t b = w5500ll_read_sock_reg(chip->spidev, 0, mode);
 		if (b != a) {
 			log_errorf("SPI to W5500 does not appear to be functional: wrote:0x%02"PRIx16" != read:0x%02"PRIx8, a, b);
 			spi_ok = false;
 		}
-	}
+	} while (a++ != 0xff);
 	if (!spi_ok)
 		__lm_abort();
 	w5500ll_write_sock_reg(chip->spidev, 0, mode, 0);
@@ -612,6 +617,7 @@ static ssize_t w5500_tcp_writev(struct _w5500_socket *socket, const struct iovec
 	ASSERT_SELF(stream_conn, TCP);
 	if (count == 0)
 		return 0;
+	assert(count <= SSIZE_MAX);
 
 	/* What we really want is to pause until we receive an ACK for
 	 * some data we just queued, so that we can line up some new
@@ -657,7 +663,7 @@ static ssize_t w5500_tcp_writev(struct _w5500_socket *socket, const struct iovec
 
 		/* Queue data to be sent.  */
 		if ((size_t)freesize > count-done)
-			freesize = count-done;
+			freesize = (uint16_t)(count-done);
 		uint16_t ptr = uint16be_unmarshal(w5500ll_read_sock_reg(chip->spidev, socknum, tx_write_pointer));
 		w5500ll_writev(chip->spidev, ptr, CTL_BLOCK_SOCK(socknum, TX), iov, iovcnt, done, freesize);
 		w5500ll_write_sock_reg(chip->spidev, socknum, tx_write_pointer, uint16be_marshal(ptr+freesize));
@@ -681,7 +687,8 @@ static ssize_t w5500_tcp_writev(struct _w5500_socket *socket, const struct iovec
 		}
 	}
 	log_debugf(" => send finished");
-	return done;
+	assert(done <= count); /* because we validated that count <= SSIZE_MAX */
+	return (ssize_t)done;
 }
 
 static void w5500_tcp_set_read_deadline(struct _w5500_socket *socket, uint64_t ns) {
@@ -759,7 +766,7 @@ static ssize_t w5500_tcp_readv(struct _w5500_socket *socket, const struct iovec
 	uint16_t ptr = uint16be_unmarshal(w5500ll_read_sock_reg(chip->spidev, socknum, rx_read_pointer));
 	/* Read the data.  */
 	if ((size_t)avail > count)
-		avail = count;
+		avail = (uint16_t)count;
 	w5500ll_readv(chip->spidev, ptr, CTL_BLOCK_SOCK(socknum, RX), iov, iovcnt, avail);
 	/* Tell the chip that we read the data.  */
 	w5500ll_write_sock_reg(chip->spidev, socknum, rx_read_pointer, uint16be_marshal(ptr+avail));
@@ -807,18 +814,19 @@ static int w5500_tcp_close_write(struct _w5500_socket *socket) { return w5500_tc
 
 /* udp_conn methods ***********************************************************/
 
-static ssize_t w5500_udp_sendto(struct _w5500_socket *socket, void *buf, size_t count,
+static ssize_t w5500_udp_sendto(struct _w5500_socket *socket, void *buf, size_t _count,
                                 struct net_ip4_addr node, uint16_t port) {
 	log_debugf("udp_conn.sendto()");
 	ASSERT_SELF(packet_conn, UDP);
 	assert(buf);
-	assert(count);
+	assert(_count);
 
 	uint16_t bufsize = ((uint16_t)w5500ll_read_sock_reg(chip->spidev, socknum, tx_buf_size))*1024;
-	if (count > bufsize) {
+	if (_count > (size_t)bufsize) {
 		log_debugf(" => msg too large");
 		return -NET_EMSGSIZE;
 	}
+	uint16_t count = (uint16_t)_count;
 
 	for (;;) {
 		cr_mutex_lock(&chip->mu);
@@ -944,7 +952,7 @@ static ssize_t w5500_udp_recvfrom(struct _w5500_socket *socket, void *buf, size_
 				.iov_len = len,
 			}), 1, 0);
 	/* Tell the chip that we read the data.  */
-	w5500ll_write_sock_reg(chip->spidev, socknum, rx_read_pointer, uint16be_marshal(ptr+8+len));
+	w5500ll_write_sock_reg(chip->spidev, socknum, rx_read_pointer, uint16be_marshal((uint16_t)(ptr+len+8)));
 	w5500_socket_cmd(socket, CMD_RECV);
 	/* Return.  */
 	LO_CALL(bootclock, del_trigger, &trigger);