Fix alignment of buffers in ra_process and dhcpv6_request

The packet buffer needs to be 32-bit aligned to ensure that the various
32-bit fields we pick out are naturally aligned.

The control message buffers needs to be naturally aligned for struct
cmsghdr.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

src/dhcpv6.c

@@ -577,7 +577,9 @@ int dhcpv6_request(enum dhcpv6_msg type)
 		// Receive rounds
 		for (; len < 0 && (round_start < round_end);
 				round_start = odhcp6c_get_milli_time()) {
-			uint8_t buf[1536], cmsg_buf[CMSG_SPACE(sizeof(struct in6_pktinfo))];
+			uint8_t buf[1536];
+			uint8_t cmsg_buf[CMSG_SPACE(sizeof(struct in6_pktinfo))]
+				__aligned(__alignof__(struct cmsghdr));
 			struct iovec iov = {buf, sizeof(buf)};
 			struct sockaddr_in6 addr;
 			struct msghdr msg = {.msg_name = &addr, .msg_namelen = sizeof(addr),

src/odhcp6c.h

@@ -18,6 +18,7 @@
 
 #define _unused __attribute__((unused))
 #define _packed __attribute__((packed))
+#define __aligned(n) __attribute__((aligned(n)))
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 

src/ra.c

@@ -274,7 +274,8 @@ bool ra_process(void)
 {
 	bool found = false;
 	bool changed = false;
-	uint8_t buf[1500], cmsg_buf[128];
+	uint8_t buf[1500] __aligned(4);
+	uint8_t cmsg_buf[128] __aligned(__alignof__(struct cmsghdr));
 	struct nd_router_advert *adv = (struct nd_router_advert*)buf;
 	struct odhcp6c_entry *entry = alloca(sizeof(*entry) + 256);
 	const struct in6_addr any = IN6ADDR_ANY_INIT;