The alloca() use in sio is incorrect. gethostby*_r will make the hostent
contain pointers to the submitted area, but when the function returns the
alloca() allocated area is freed. Always use the supplied buffer.

diff -ru ncftp-3.2.5.orig/sio/DNSUtil.c ncftp-3.2.5/sio/DNSUtil.c
--- ncftp-3.2.5.orig/sio/DNSUtil.c	2009-10-24 02:31:23.000000000 +0300
+++ ncftp-3.2.5/sio/DNSUtil.c	2016-03-22 16:17:36.809816988 +0200
@@ -50,6 +50,13 @@
 			errno = ENOENT;
 		break;
 	}
+#elif defined(HAVE_GETHOSTBYNAME_R) && defined(LINUX)
+	struct hostent *h;
+	int h_errno_unused = 0, r;
+	memset(hpbuf, 0, hpbufsize);
+	r = gethostbyname_r(name, hp, hpbuf, hpbufsize, &h, &h_errno_unused);
+	if (r == 0 && h != NULL)
+		return (0);
 #elif defined(HAVE_GETHOSTBYNAME_R) && (defined(SOLARIS) || defined(IRIX) || defined(BSDOS))
 	struct hostent *h;
 	int h_errno_unused = 0;
@@ -57,60 +64,6 @@
 	h = gethostbyname_r(name, hp, hpbuf, hpbufsize, &h_errno_unused);
 	if (h != NULL)
 		return (0);
-#elif defined(HAVE_GETHOSTBYNAME2_R) && defined(LINUX) && defined(HAVE_ALLOCA)
-	char *usehpbuf;
-	struct hostent *h;
-	int my_h_errno, rc;
-
-	usehpbuf = hpbuf;
-	forever {
-		errno = 0;
-		my_h_errno = 0;
-		h = NULL;
-		memset(usehpbuf, 0, hpbufsize);
-		rc = gethostbyname2_r(name, AF_INET, hp, usehpbuf, hpbufsize, &h, &my_h_errno);
-		if ((rc == 0) && (h != NULL))
-			return (0);
-		if ((rc == ERANGE) || ((rc == -1) && (errno == ERANGE))) {
-			hpbufsize *= 2;
-			usehpbuf = alloca(hpbufsize);
-			if (usehpbuf == NULL) {
-				errno = ENOMEM;
-				return (-1);
-			}
-			continue;
-		}
-		if ((rc == 0) && (my_h_errno != 0))
-			errno = ENOENT;
-		break;
-	}
-#elif defined(HAVE_GETHOSTBYNAME_R) && defined(LINUX) && defined(HAVE_ALLOCA)
-	char *usehpbuf;
-	struct hostent *h;
-	int my_h_errno, rc;
-
-	usehpbuf = hpbuf;
-	forever {
-		errno = 0;
-		my_h_errno = 0;
-		h = NULL;
-		memset(usehpbuf, 0, hpbufsize);
-		rc = gethostbyname_r(name, hp, usehpbuf, hpbufsize, &h, &my_h_errno);
-		if ((rc == 0) && (h != NULL))
-			return (0);
-		if ((rc == ERANGE) || ((rc == -1) && (errno == ERANGE))) {
-			hpbufsize *= 2;
-			usehpbuf = alloca(hpbufsize);
-			if (usehpbuf == NULL) {
-				errno = ENOMEM;
-				return (-1);
-			}
-			continue;
-		}
-		if ((rc == 0) && (my_h_errno != 0))
-			errno = ENOENT;
-		break;
-	}
 #elif defined(HAVE_GETHOSTBYNAME_R) && defined(AIX)
 	struct hostent_data hed;
 	memset(hpbuf, 0, hpbufsize);
@@ -152,6 +105,13 @@
 			return (-2);
 		return (0);
 	}
+#elif defined(HAVE_GETHOSTBYADDR_R) && defined(LINUX)
+	struct hostent *h;
+	int h_errno_unused = 0, r;
+	memset(hpbuf, 0, hpbufsize);
+	r = gethostbyaddr_r((const void *) addr, asize, atype, hp, hpbuf, hpbufsize, &h, &h_errno_unused);
+	if (r == 0 && h != NULL)
+		return (0);
 #elif defined(HAVE_GETHOSTBYADDR_R) && (defined(SOLARIS) || defined(IRIX) || defined(BSDOS))
 	struct hostent *h;
 	int h_errno_unused = 0;
@@ -159,33 +119,6 @@
 	h = gethostbyaddr_r((gethost_addrptr_t) addr, asize, atype, hp, hpbuf, hpbufsize, &h_errno_unused);
 	if (h != NULL)
 		return (0);
-#elif defined(HAVE_GETHOSTBYADDR_R) && defined(LINUX) && defined(HAVE_ALLOCA)
-	char *usehpbuf;
-	struct hostent *h;
-	int my_h_errno, rc;
-
-	usehpbuf = hpbuf;
-	forever {
-		errno = 0;
-		my_h_errno = 0;
-		h = NULL;
-		memset(usehpbuf, 0, hpbufsize);
-		rc = gethostbyaddr_r((gethost_addrptr_t) addr, asize, atype, hp, usehpbuf, hpbufsize, &h, &my_h_errno);
-		if ((rc == 0) && (h != NULL))
-			return (0);
-		if ((rc == ERANGE) || ((rc == -1) && (errno == ERANGE))) {
-			hpbufsize *= 2;
-			usehpbuf = alloca(hpbufsize);
-			if (usehpbuf == NULL) {
-				errno = ENOMEM;
-				return (-1);
-			}
-			continue;
-		}
-		if ((rc == 0) && (my_h_errno != 0))
-			errno = ENOENT;
-		break;
-	}
 #elif defined(HAVE_GETHOSTBYADDR_R) && defined(AIX)
 	struct hostent_data hed;
 	memset(hpbuf, 0, hpbufsize);