From 25db34ffae569e9ff78fd3f5f6f621ee73da9a2f Mon Sep 17 00:00:00 2001
From: deraadt <>
Date: Thu, 8 Jul 1999 22:29:53 +0000
Subject: use SIOCGIFCONF much more carefully

---
 src/lib/libc/net/if_nameindex.c | 48 +++++++++++++++++++++++++++++------------
 1 file changed, 34 insertions(+), 14 deletions(-)

(limited to 'src/lib/libc/net/if_nameindex.c')

diff --git a/src/lib/libc/net/if_nameindex.c b/src/lib/libc/net/if_nameindex.c
index 8714c1f95a..8643397db2 100644
--- a/src/lib/libc/net/if_nameindex.c
+++ b/src/lib/libc/net/if_nameindex.c
@@ -43,29 +43,48 @@
 struct if_nameindex *
 if_nameindex(void)
 {
-	int     i, j, fd, len;
+	int     i, j, fd = -1, extra, len = 0;
 	struct if_nameindex *nameindex = NULL;
 	struct ifconf ifconf;
-	char    lastname[IFNAMSIZ], *c;
+	char    lastname[IFNAMSIZ], *c, *inbuf;
 	struct if_nameindex *n;
 	struct sockaddr_dl *sd;
 	struct sockaddr *sa;
 	void   *p;
 
-	if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
-		return NULL;
+	ifconf.ifc_buf = NULL;
 
-	ifconf.ifc_len = 0;
-	ifconf.ifc_buf = 0;
-	if (ioctl(fd, SIOCGIFCONF, (void *) &ifconf))
-		goto ret;
-	if (ifconf.ifc_len < IFNAMSIZ)
-		goto ret;
-	if (!(ifconf.ifc_buf = malloc(ifconf.ifc_len)))
-		goto ret;
-	if (ioctl(fd, SIOCGIFCONF, (void *) &ifconf))
+	if ((fd = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
 		goto ret;
 
+	/*
+	 * Try ifc_len == 0 hack first, to get the actual length.
+	 * If that fails, revert to a loop which grows the ifc_buf
+	 * until it is sufficiently large.
+	 */
+	extra = sizeof(struct ifreq);
+	while (1) {
+		ifconf.ifc_len = len;
+		if (ioctl(fd, SIOCGIFCONF, (void *) &ifconf) == -1 &&
+		    ifconf.ifc_buf)
+			goto ret;
+		if (ifconf.ifc_buf &&
+		    ifconf.ifc_len + extra < len)
+			break;
+		if (ifconf.ifc_buf) {
+			if (len == 0)
+				len = 4096;
+			ifconf.ifc_len = len *= 2;
+		} else {
+			len = ifconf.ifc_len;
+			extra = 0;
+		}
+		inbuf = realloc(ifconf.ifc_buf, ifconf.ifc_len);
+		if (inbuf == NULL)
+			goto ret;
+		ifconf.ifc_buf = inbuf;
+	}
+
 	i = sizeof(struct if_nameindex);
 	j = 0;
 	p = ifconf.ifc_buf;
@@ -138,7 +157,8 @@ if_nameindex(void)
 		n->if_index = i;
 
 ret:
-	close(fd);
+	if (fd != -1)
+		close(fd);
 	if (ifconf.ifc_buf)
 		free(ifconf.ifc_buf);
 	return (nameindex);
-- 
cgit v1.2.3-55-g6feb