From d146e98b7f94940386f60a902031b2a9b6237730 Mon Sep 17 00:00:00 2001
From: Tom Stellard <tstellar@redhat.com>
Date: Tue, 4 Jul 2017 16:03:34 +0000
Subject: [PATCH] ELF: Only unlink regular files

Summary:
If the output file is a character file (e.g. /dev/null) unlinking it could
potentially destabilize the user's system.  For example,
unlinking causes `lld %input -o /dev/null` to replace /dev/null with a
regular file, which will lead to unexpected behavior in other programs
that read from /dev/null, and worse than expected peformance for
programs that write to /dev/null.

This makes it possible to run the test-release.sh script as root.
Prior to this patch, the ELF/basic.s test would replace
/dev/null with a regular file, which would cause crashes in llvm
test-suite programs that piped /dev/null to stdin.

For example, if you run the test-relase.sh script as root,

Reviewers: ruiu

Reviewed By: ruiu

Subscribers: emaste, llvm-commits

Differential Revision: https://reviews.llvm.org/D34917
---
 ELF/Writer.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ELF/Writer.cpp b/ELF/Writer.cpp
index b004a4f..d52165b 100644
--- a/ELF/Writer.cpp
+++ b/ELF/Writer.cpp
@@ -1650,7 +1650,8 @@ template <class ELFT> void Writer<ELFT>::writeHeader() {
 // This function spawns a background thread to call unlink.
 // The calling thread returns almost immediately.
 static void unlinkAsync(StringRef Path) {
-  if (!Config->Threads || !sys::fs::exists(Config->OutputFile))
+  if (!Config->Threads || !sys::fs::exists(Config->OutputFile) ||
+      !sys::fs::is_regular_file(Config->OutputFile))
     return;
 
   // First, rename Path to avoid race condition. We cannot remove
-- 
1.8.3.1