io: Add crash guards

Signed-off-by: Hiroshi Hatake <hiroshi@chronosphere.io>

Author: cosmo0920

src/flb_io.c

@@ -726,6 +726,17 @@ int flb_io_net_writev(struct flb_connection *connection,
     total_length = 0;
 
     for (index = 0 ; index < iovcnt ; index++) {
+        /* Overflow guard */
+        if (iov[index].iov_len > SIZE_MAX - total_length) {
+            errno = EOVERFLOW;
+            return -1;
+        }
+
+        if (iov[index].iov_len > 0 && iov[index].iov_base == NULL) {
+            errno = EINVAL;
+            return -1;
+        }
+
         total_length += iov[index].iov_len;
     }