From d5e1bffd2a5b5c39f14944fe3ba25414dcd0d508 Mon Sep 17 00:00:00 2001
From: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
Date: Tue, 18 Jul 2017 17:51:50 -0400
Subject: [PATCH] Do not try to fill fd_set with fd>=FD_SETSIZE

This is UB and causes buffer overflow and crash on linux.
---
 src/libstore/build.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 60b0a531f..d2a270259 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -3835,6 +3835,9 @@ void Worker::waitForInput()
     int fdMax = 0;
     for (auto & i : children) {
         for (auto & j : i.fds) {
+            if (j >= FD_SETSIZE) {
+                throw BuildError("reached FD_SETSIZE limit");
+            }
             FD_SET(j, &fds);
             if (j >= fdMax) fdMax = j + 1;
         }