rework netlink_get_interface_ip to handle large recvfrom() responses

without doing its own buffering or leaking memory.

1 files changed, 18 insertions, 23 deletions

diff --git a/isys/nl.c b/isys/nl.c
index 0d19ad038..771ee2947 100644
--- a/isys/nl.c
+++ b/isys/nl.c
@@ -257,7 +257,8 @@ int netlink_get_interface_ip(int index, int family, void *addr) {
  * @return 0 on succes, -1 on error.
  */
 int netlink_init_interfaces_list(void) {
-    int sock, len, alen, r, bufsz, readsz, havemsg, namelen;
+    int sock, len, alen, r, namelen;
+    ssize_t bufsz, readsz;
     char *buf = NULL;
     struct nlmsghdr *nlh;
     struct ifinfomsg *ifi;
@@ -283,34 +284,28 @@ int netlink_init_interfaces_list(void) {
         return -1;
     }
 
-    /* read back messages */
-    if ((buf = calloc(BUFSZ, sizeof(char))) == NULL) {
-        perror("calloc on 1st buf in netlink_init_interfaces_list");
+    while ((bufsz = recvfrom(sock, NULL, 0, MSG_PEEK|MSG_TRUNC|MSG_WAITALL,
+                    NULL, 0)) <= 0) {
+        if (bufsz < 0 && errno != EAGAIN) {
+            perror("1st recvfrom in netlink_init_interfaces_list");
+            close(sock);
+            return -1;
+        }
+    }
+
+    if ((buf = alloca(bufsz)) == NULL) {
+        perror("calloc on msg buf in netlink_init_interfaces_list");
         close(sock);
         return -1;
     }
+    memset(buf, '\0', bufsz);
 
-    havemsg = 0;
-    readsz = BUFSZ;
-    while (!havemsg) {
-        bufsz = recvfrom(sock, buf, readsz, 0, NULL, 0);
-
-        if (bufsz < 0) {
-            perror("recvfrom in netlink_init_interfaces_list");
+    recvfrom(sock, buf, bufsz, 0, NULL, 0);
+    while ((readsz = recvfrom(sock, buf, bufsz, MSG_WAITALL, NULL, 0)) < 0) {
+        if (errno != EAGAIN) {
+            perror("2nd recvfrom in netlink_init_interfaces_list");
             close(sock);
             return -1;
-        } else if (bufsz > readsz) {
-            free(buf);
-            buf = NULL;
-
-            readsz = bufsz;
-            if ((buf = calloc(readsz, sizeof(char))) == NULL) {
-                perror("calloc on 2nd buf in netlink_init_interfaces_list");
-                close(sock);
-                return -1;
-            }
-        } else  {
-            havemsg = 1;
         }
     }