Check for bad packets in getaddrinfo.c's getanswer.

The near duplicate in gethnamaddr.c was already doing so (this fix
is basically copy and pasted from there, but with both copies modified
to avoid skirting undefined behavior).

Bug: 32322088
Test: browser still works
Change-Id: Ied6662be567fb1bddc7ceb138cae1da77fb57976
(cherry picked from commit 27a4459d945e34fabd7166791a5b862ccea83f23)
(cherry picked from commit 418fe1e)
(cherry picked from commit 0f6bfb7068224ecc7e80c9b91bffa3dfa912b4e9)

Author: enh-google

libc/netbsd/gethnamaddr.c

@@ -159,15 +159,12 @@ dprintf(const char *msg, res_state res, ...)
 #define BOUNDED_INCR(x) \
 	do { \
 		cp += (x); \
-		if (cp > eom) { \
-			h_errno = NO_RECOVERY; \
-			return NULL; \
-		} \
+		BOUNDS_CHECK(cp, x); \
 	} while (/*CONSTCOND*/0)
 
 #define BOUNDS_CHECK(ptr, count) \
 	do { \
-		if ((ptr) + (count) > eom) { \
+		if (eom - (ptr) < (count)) {\
 			h_errno = NO_RECOVERY; \
 			return NULL; \
 		} \

libc/netbsd/net/getaddrinfo.c

@@ -1292,6 +1292,17 @@ ip6_str2scopeid(char *scope, struct sockaddr_in6 *sin6, u_int32_t *scopeid)
 static const char AskedForGot[] =
 	"gethostby*.getanswer: asked for \"%s\", got \"%s\"";
 
+#define BOUNDED_INCR(x) \
+	do { \
+		BOUNDS_CHECK(cp, x); \
+		cp += (x); \
+	} while (/*CONSTCOND*/0)
+
+#define BOUNDS_CHECK(ptr, count) \
+	do { \
+		if (eom - (ptr) < (count)) { h_errno = NO_RECOVERY; return NULL; } \
+	} while (/*CONSTCOND*/0)
+
 static struct addrinfo *
 getanswer(const querybuf *answer, int anslen, const char *qname, int qtype,
     const struct addrinfo *pai)
@@ -1337,7 +1348,8 @@ getanswer(const querybuf *answer, int anslen, const char *qname, int qtype,
 	qdcount = ntohs(hp->qdcount);
 	bp = hostbuf;
 	ep = hostbuf + sizeof hostbuf;
-	cp = answer->buf + HFIXEDSZ;
+	cp = answer->buf;
+	BOUNDED_INCR(HFIXEDSZ);
 	if (qdcount != 1) {
 		h_errno = NO_RECOVERY;
 		return (NULL);
@@ -1347,7 +1359,7 @@ getanswer(const querybuf *answer, int anslen, const char *qname, int qtype,
 		h_errno = NO_RECOVERY;
 		return (NULL);
 	}
-	cp += n + QFIXEDSZ;
+	BOUNDED_INCR(n + QFIXEDSZ);
 	if (qtype == T_A || qtype == T_AAAA || qtype == T_ANY) {
 		/* res_send() has already verified that the query name is the
 		 * same as the one we sent; this just gets the expanded name
@@ -1372,12 +1384,14 @@ getanswer(const querybuf *answer, int anslen, const char *qname, int qtype,
 			continue;
 		}
 		cp += n;			/* name */
+		BOUNDS_CHECK(cp, 3 * INT16SZ + INT32SZ);
 		type = _getshort(cp);
  		cp += INT16SZ;			/* type */
 		class = _getshort(cp);
  		cp += INT16SZ + INT32SZ;	/* class, TTL */
 		n = _getshort(cp);
 		cp += INT16SZ;			/* len */
+		BOUNDS_CHECK(cp, n);
 		if (class != C_IN) {
 			/* XXX - debug? syslog? */
 			cp += n;