[clang] Fix out-of-bounds memory access in ComputeLineNumbers

Differential Revision: https://reviews.llvm.org/D72409

1 files changed, 8 insertions, 13 deletions

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index 5f457d6f9e3..73f2ae96d4a 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -1250,23 +1250,18 @@ static void ComputeLineNumbers(DiagnosticsEngine &Diag, ContentCache *FI,
 
   const unsigned char *Buf = (const unsigned char *)Buffer->getBufferStart();
   const unsigned char *End = (const unsigned char *)Buffer->getBufferEnd();
+  const std::size_t BufLen = End - Buf;
   unsigned I = 0;
-  while (true) {
-    // Skip over the contents of the line.
-    while (Buf[I] != '\n' && Buf[I] != '\r' && Buf[I] != '\0')
-      ++I;
-
-    if (Buf[I] == '\n' || Buf[I] == '\r') {
+  while (I < BufLen) {
+    if (Buf[I] == '\n') {
+      LineOffsets.push_back(I + 1);
+    } else if (Buf[I] == '\r') {
       // If this is \r\n, skip both characters.
-      if (Buf[I] == '\r' && Buf[I+1] == '\n')
+      if (I + 1 < BufLen && Buf[I + 1] == '\n')
         ++I;
-      ++I;
-      LineOffsets.push_back(I);
-    } else {
-      // Otherwise, this is a NUL. If end of file, exit.
-      if (Buf+I == End) break;
-      ++I;
+      LineOffsets.push_back(I + 1);
     }
+    ++I;
   }
 
   // Copy the offsets into the FileInfo structure.