From af86132e1afa65b4b466af3ea9c7084836c91ee0 Mon Sep 17 00:00:00 2001
From: Tuomas Tynkkynen <tuomas@tuxera.com>
Date: Tue, 3 Apr 2018 15:27:17 +0300
Subject: libexpr: Make unsafeGetAttrPos not crash on noPos

Currently e.g. `builtins.unsafeGetAttrPos "abort" builtins` will
eventually segfault because pos->file is an unset Symbol.

Found by afl-fuzz.
---
 src/libexpr/eval.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'src/libexpr')

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 37b977736..854899079 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -628,7 +628,7 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 
 void EvalState::mkPos(Value & v, Pos * pos)
 {
-    if (pos) {
+    if (pos && pos->file.set()) {
         mkAttrs(v, 3);
         mkString(*allocAttr(v, sFile), pos->file);
         mkInt(*allocAttr(v, sLine), pos->line);
-- 
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