resolv: Fix unaligned accesses to fields in HEADER struct

The structure HEADER is normally aligned to a word boundary but
sometimes it needs to be accessed when aligned on a byte boundary.
This change defines a new typedef, UHEADER, with alignment 1.
It is used to ensure the fields are accessed with byte loads and
stores when necessary.

V4: Change to res_mkquery.c deleted.  Small whitespace fix.

V5: Move UHEADER typedef to resolv/resolv-internal.h.  Replace all
HEADER usage with UHEADER in resolv/res_send.c.

Dave
---

diff --git a/resolv/res_query.c b/resolv/res_query.c
index 5d0a68dc81..3b5c604261 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -112,8 +112,8 @@ __res_context_query (struct resolv_context *ctx, const char *name,
 		     int *nanswerp2, int *resplen2, int *answerp2_malloced)
 {
 	struct __res_state *statp = ctx->resp;
-	HEADER *hp = (HEADER *) answer;
-	HEADER *hp2;
+	UHEADER *hp = (UHEADER *) answer;
+	UHEADER *hp2;
 	int n, use_malloc = 0;
 
 	size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
@@ -217,7 +217,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
 
 	if (answerp != NULL)
 	  /* __res_context_send might have reallocated the buffer.  */
-	  hp = (HEADER *) *answerp;
+	  hp = (UHEADER *) *answerp;
 
 	/* We simplify the following tests by assigning HP to HP2 or
 	   vice versa.  It is easy to verify that this is the same as
@@ -228,7 +228,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
 	  }
 	else
 	  {
-	    hp2 = (HEADER *) *answerp2;
+	    hp2 = (UHEADER *) *answerp2;
 	    if (n < (int) sizeof (HEADER))
 	      {
 	        hp = hp2;
@@ -338,7 +338,7 @@ __res_context_search (struct resolv_context *ctx,
 {
 	struct __res_state *statp = ctx->resp;
 	const char *cp;
-	HEADER *hp = (HEADER *) answer;
+	UHEADER *hp = (UHEADER *) answer;
 	char tmp[NS_MAXDNAME];
 	u_int dots;
 	int trailing_dot, ret, saved_herrno;
diff --git a/resolv/res_send.c b/resolv/res_send.c
index 5d6be4b82d..d6c85fd7a2 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -245,7 +245,7 @@ static void
 mask_ad_bit (struct resolv_context *ctx, void *buf)
 {
   if (!(ctx->resp->options & RES_TRUSTAD))
-    ((HEADER *) buf)->ad = 0;
+    ((UHEADER *) buf)->ad = 0;
 }
 
 int
@@ -560,9 +560,9 @@ send_vc(res_state statp,
 	int *terrno, int ns, u_char **anscp, u_char **ansp2, int *anssizp2,
 	int *resplen2, int *ansp2_malloced)
 {
-	const HEADER *hp = (HEADER *) buf;
-	const HEADER *hp2 = (HEADER *) buf2;
-	HEADER *anhp = (HEADER *) *ansp;
+	const UHEADER *hp = (UHEADER *) buf;
+	const UHEADER *hp2 = (UHEADER *) buf2;
+	UHEADER *anhp = (UHEADER *) *ansp;
 	struct sockaddr *nsap = __res_get_nsaddr (statp, ns);
 	int truncating, connreset, n;
 	/* On some architectures compiler might emit a warning indicating
@@ -697,7 +697,7 @@ send_vc(res_state statp,
 		thisansp = ansp2;
 		thisresplenp = resplen2;
 	}
-	anhp = (HEADER *) *thisansp;
+	anhp = (UHEADER *) *thisansp;
 
 	*thisresplenp = rlen;
 	/* Is the answer buffer too small?  */
@@ -718,7 +718,7 @@ send_vc(res_state statp,
 			*thisansp = newp;
 			if (thisansp == ansp2)
 			  *ansp2_malloced = 1;
-			anhp = (HEADER *) newp;
+			anhp = (UHEADER *) newp;
 			/* A uint16_t can't be larger than MAXPACKET
 			   thus it's safe to allocate MAXPACKET but
 			   read RLEN bytes instead.  */
@@ -925,8 +925,8 @@ send_dg(res_state statp,
 	int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp,
 	u_char **ansp2, int *anssizp2, int *resplen2, int *ansp2_malloced)
 {
-	const HEADER *hp = (HEADER *) buf;
-	const HEADER *hp2 = (HEADER *) buf2;
+	const UHEADER *hp = (UHEADER *) buf;
+	const UHEADER *hp2 = (UHEADER *) buf2;
 	struct timespec now, timeout, finish;
 	struct pollfd pfd[1];
 	int ptimeout;
@@ -1168,7 +1168,7 @@ send_dg(res_state statp,
 		   MSG_TRUNC which is only available on Linux.  We
 		   can abstract out the Linux-specific feature in the
 		   future to detect truncation.  */
-		HEADER *anhp = (HEADER *) *thisansp;
+		UHEADER *anhp = (UHEADER *) *thisansp;
 		socklen_t fromlen = sizeof(struct sockaddr_in6);
 		assert (sizeof(from) <= fromlen);
 		*thisresplenp = __recvfrom (pfd[0].fd, (char *) *thisansp,
diff --git a/resolv/resolv-internal.h b/resolv/resolv-internal.h
index 2fa57d394f..9d2e832d68 100644
--- a/resolv/resolv-internal.h
+++ b/resolv/resolv-internal.h
@@ -27,6 +27,13 @@
 #define RES_F_CONN      0x00000002 /* Socket is connected.  */
 #define RES_F_EDNS0ERR  0x00000004 /* EDNS0 caused errors.  */
 
+/* The structure HEADER is normally aligned on a word boundary.  In
+   some code, we need to access this structure when it may be aligned
+   on a byte boundary.  To avoid unaligned accesses, we need a typedef
+   with alignment one.  This ensures the fields are accessed with byte
+   loads and stores.  */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+
 /* Legacy function.  This needs to be removed once all NSS modules
    have been adjusted.  */
 static inline bool