Fix strict aliasing violation in inet_checksum()

inet_checksum() accesses packet data as an array of uint16_t, but the
packet data can be for example of "anonymous struct pseudo" type from
route_ipv6_unreachable().
This type isn't a compatible type with uint16_t so a strict aliasing
violation occurs and causes the checksum to be computed incorrectly.

Fix this by using the memcpy() idiom to read the packet data as an array of
uint16_t in inet_checksum() (this should be understood by compilers and
optimized accordingly, so no actual copy occurs).

diff --git a/src/route.c b/src/route.c
index 2e8d94a..2fa6175 100644 (file)
--- a/src/route.c
+++ b/src/route.c
@@ -64,16 +64,18 @@ static timeout_t age_subnets_timeout;
 /* RFC 1071 */
 
 static uint16_t inet_checksum(void *data, int len, uint16_t prevsum) {
-       uint16_t *p = data;
+       uint16_t word;
        uint32_t checksum = prevsum ^ 0xFFFF;
 
        while(len >= 2) {
-               checksum += *p++;
+               memcpy(&word, data, sizeof(word));
+               checksum += word;
+               data += 2;
                len -= 2;
        }
 
        if(len) {
-               checksum += *(uint8_t *)p;
+               checksum += *(uint8_t *)data;
        }
 
        while(checksum >> 16) {