From d24a34857afc33ed11da9ba62736c0bb9b3e5b94 Mon Sep 17 00:00:00 2001
From: Rolf Eike Beer <eike@sf-mail.de>
Date: Thu, 29 Aug 2019 20:35:48 +0200
Subject: [PATCH 1/2] ask kernel for the correct buffer size to satisfy
 SIOCGIFCONF before looping

---
 ipme.c | 41 ++++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/ipme.c b/ipme.c
index 3c86127..d88785d 100644
--- a/ipme.c
+++ b/ipme.c
@@ -52,20 +52,35 @@ int ipme_init()
   byte_copy(&ix.ip,4,"\0\0\0\0");
   if (!ipalloc_append(&ipme,&ix)) { return 0; }
   if ((s = socket(AF_INET,SOCK_STREAM,0)) == -1) return -1;
- 
-  len = 256;
-  for (;;) {
-    if (!stralloc_ready(&buf,len)) { close(s); return 0; }
-    buf.len = 0;
+
+  ifc.ifc_buf = 0;
+  ifc.ifc_len = 0;
+
+  /* first pass: just ask what the correct length for all addresses is */
+  len = 0;
+  if (ioctl(s,SIOCGIFCONF,&ifc) >= 0 && ifc.ifc_len > 0) { /* > is for System V */
+    if (!stralloc_ready(&buf,ifc.ifc_len)) { close(s); return 0; }
     ifc.ifc_buf = buf.s;
-    ifc.ifc_len = len;
-    if (ioctl(s,SIOCGIFCONF,&ifc) >= 0) /* > is for System V */
-      if (ifc.ifc_len + sizeof(*ifr) + 64 < len) { /* what a stupid interface */
-        buf.len = ifc.ifc_len;
-        break;
-      }
-    if (len > 200000) { close(s); return -1; }
-    len += 100 + (len >> 2);
+    if (ioctl(s,SIOCGIFCONF,&ifc) >= 0)
+      buf.len = ifc.ifc_len;
+  }
+
+  /* check if we have complete length, otherwise try so sort that out */
+  if (buf.len == 0) {
+    len = 256;
+    for (;;) {
+      if (!stralloc_ready(&buf,len)) { close(s); return 0; }
+      buf.len = 0;
+      ifc.ifc_buf = buf.s;
+      ifc.ifc_len = len;
+      if (ioctl(s,SIOCGIFCONF,&ifc) >= 0) /* > is for System V */
+        if (ifc.ifc_len + sizeof(*ifr) + 64 < len) { /* what a stupid interface */
+          buf.len = ifc.ifc_len;
+          break;
+        }
+      if (len > 200000) { close(s); return -1; }
+      len += 100 + (len >> 2);
+    }
   }
   x = buf.s;
   while (x < buf.s + buf.len) {
-- 
2.16.4

From 9d6c05d092e3cf94a6591cd5420f8026fcd4691f Mon Sep 17 00:00:00 2001
From: Rolf Eike Beer <eike@sf-mail.de>
Date: Thu, 29 Aug 2019 20:37:03 +0200
Subject: [PATCH 2/2] ipme: fix detection of multiple IP addresses on the same
 link

The problem was that the code did another ioctl() to check if the link is
actually up, and when doing this overwrites the information it is currently
looking at. The code when sa_len is available copies the current IP address out
before checking if the link is up. Reorder the code so both branches share more
code and both work.
---
 CHANGES |  2 ++
 ipme.c  | 14 +++-----------
 2 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/ipme.c b/ipme.c
index d88785d..e163f5b 100644
--- a/ipme.c
+++ b/ipme.c
@@ -89,6 +89,9 @@ int ipme_init()
     len = sizeof(ifr->ifr_name) + ifr->ifr_addr.sa_len;
     if (len < sizeof(*ifr))
       len = sizeof(*ifr);
+#else
+    len = sizeof(*ifr);
+#endif
     if (ifr->ifr_addr.sa_family == AF_INET) {
       sin = (struct sockaddr_in *) &ifr->ifr_addr;
       byte_copy(&ix.ip,4,&sin->sin_addr);
@@ -96,17 +99,6 @@ int ipme_init()
         if (ifr->ifr_flags & IFF_UP)
           if (!ipalloc_append(&ipme,&ix)) { close(s); return 0; }
     }
-#else
-    len = sizeof(*ifr);
-    if (ioctl(s,SIOCGIFFLAGS,x) == 0)
-      if (ifr->ifr_flags & IFF_UP)
-        if (ioctl(s,SIOCGIFADDR,x) == 0)
-	  if (ifr->ifr_addr.sa_family == AF_INET) {
-	    sin = (struct sockaddr_in *) &ifr->ifr_addr;
-	    byte_copy(&ix.ip,4,&sin->sin_addr);
-	    if (!ipalloc_append(&ipme,&ix)) { close(s); return 0; }
-	  }
-#endif
     x += len;
   }
   close(s);
-- 
2.16.4