Bug fix: Fix undefined behavior of ipv4_t type.

Turns out unions that include arrays and a integer can have UB due to
endianess not being the same across systems.

1 files changed, 19 insertions, 25 deletions

diff --git a/kernel/network/ipv4.c b/kernel/network/ipv4.c
index 8fb983a..69ceef7 100644
--- a/kernel/network/ipv4.c
+++ b/kernel/network/ipv4.c
@@ -9,27 +9,13 @@
 #include <network/udp.h>
 #include <string.h>
 
-u16 ip_checksum(void *vdata, size_t length) {
-  // Cast the data pointer to one that can be indexed.
-  char *data = (char *)vdata;
-
+static u16 ip_checksum(const u16 *data, u16 length) {
   // Initialise the accumulator.
   u32 acc = 0xffff;
 
   // Handle complete 16-bit blocks.
-  for (size_t i = 0; i + 1 < length; i += 2) {
-    u16 word;
-    memcpy(&word, data + i, 2);
-    acc += ntohs(word);
-    if (acc > 0xffff) {
-      acc -= 0xffff;
-    }
-  }
-
-  // Handle any partial block at the end of the data.
-  if (length & 1) {
-    u16 word = 0;
-    memcpy(&word, data + length - 1, 1);
+  for (size_t i = 0; i < length / 2; i++) {
+    u16 word = *(data + i);
     acc += ntohs(word);
     if (acc > 0xffff) {
       acc -= 0xffff;
@@ -41,16 +27,24 @@ u16 ip_checksum(void *vdata, size_t length) {
 }
 
 void send_ipv4_packet(ipv4_t ip, u8 protocol, const u8 *payload, u16 length) {
-  u8 header[20] = {0};
+  u16 header[10];
   header[0] = (4 /*version*/ << 4) | (5 /*IHL*/);
-  *((u16 *)(header + 2)) = htons(length + 20);
-  header[8 /*TTL*/] = 0xF8;
-  header[9] = protocol;
 
-  memcpy(header + 12 /*src_ip*/, &ip_address, sizeof(ipv4_t));
-  memcpy(header + 16, &ip, sizeof(ipv4_t));
+  header[1] = htons(length + 20);
+
+  header[2] = 0;
+
+  header[3] = 0;
+  header[4] = (protocol << 8) | 0xF8;
+
+  header[5] = 0;
+  header[6] = (ip_address.d >> 0) & 0xFFFF;
+  header[7] = (ip_address.d >> 16) & 0xFFFF;
+
+  header[8] = (ip.d >> 0) & 0xFFFF;
+  header[9] = (ip.d >> 16) & 0xFFFF;
 
-  *((u16 *)(header + 10 /*checksum*/)) = ip_checksum(header, 20);
+  header[5] = ip_checksum(header, 20);
   u16 packet_length = length + 20;
   u8 *packet = kmalloc(packet_length);
   memcpy(packet, header, 20);
@@ -68,7 +62,7 @@ void handle_ipv4(const u8 *payload, u32 packet_length) {
 
   u16 saved_checksum = *(u16 *)(payload + 10);
   *(u16 *)(payload + 10) = 0;
-  u16 calc_checksum = ip_checksum((u8 *)payload, 20);
+  u16 calc_checksum = ip_checksum((const u16 *)payload, 20);
   *(u16 *)(payload + 10) = saved_checksum;
   if (calc_checksum != saved_checksum) {
     klog(LOG_WARN, "Invalid ipv4 checksum");