Fix input validation issues in llvm-as/llvm-dis

Summary:
1. llvm-as/llvm-dis tools do not check for input filename length.
2. llvm-dis does not verify the `Streamer` variable against `nullptr` properly, so the `M` variable could be uninitialized (e.g. if the input file does not exist) leading to null dref.

Patch by Lenar Safin!

Reviewers: samsonov

Reviewed By: samsonov

Subscribers: samsonov, llvm-commits

Differential Revision: http://reviews.llvm.org/D9584

llvm-svn: 237051

1 files changed, 2 insertions, 8 deletions

diff --git a/llvm/tools/llvm-as/llvm-as.cpp b/llvm/tools/llvm-as/llvm-as.cpp
index c6b3f934202..4455d24fb60 100644
--- a/llvm/tools/llvm-as/llvm-as.cpp
+++ b/llvm/tools/llvm-as/llvm-as.cpp
@@ -62,14 +62,8 @@ static void WriteOutputFile(const Module *M) {
     if (InputFilename == "-") {
       OutputFilename = "-";
     } else {
-      std::string IFN = InputFilename;
-      int Len = IFN.length();
-      if (IFN[Len-3] == '.' && IFN[Len-2] == 'l' && IFN[Len-1] == 'l') {
-        // Source ends in .ll
-        OutputFilename = std::string(IFN.begin(), IFN.end()-3);
-      } else {
-        OutputFilename = IFN;   // Append a .bc to it
-      }
+      StringRef IFN = InputFilename;
+      OutputFilename = (IFN.endswith(".ll") ? IFN.drop_back(3) : IFN).str();
       OutputFilename += ".bc";
     }
   }