[CodeView] Take the StreamRef::readBytes offset into account when validating

We only considered the length of the operation and the length of the
StreamRef without considered what it meant for the offset to be at a
non-zero position.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271496 91177308-0d34-0410-b5e6-96231b3b80d8

Author: majnemer

include/llvm/DebugInfo/CodeView/StreamRef.h

@@ -29,7 +29,7 @@ class StreamRef : public StreamInterface {
 
   Error readBytes(uint32_t Offset, uint32_t Size,
                   ArrayRef<uint8_t> &Buffer) const override {
-    if (Size > Length)
+    if (Size + Offset > Length)
       return make_error<CodeViewError>(cv_error_code::insufficient_buffer);
     return Stream->readBytes(ViewOffset + Offset, Size, Buffer);
   }

unittests/DebugInfo/PDB/MappedBlockStreamTest.cpp

@@ -79,6 +79,8 @@ TEST(MappedBlockStreamTest, ReadBeyondEndOfStreamRef) {
   EXPECT_NO_ERROR(R.readStreamRef(SR, 0U));
   ArrayRef<uint8_t> Buffer;
   EXPECT_ERROR(SR.readBytes(0U, 1U, Buffer));
+  EXPECT_NO_ERROR(R.readStreamRef(SR, 1U));
+  EXPECT_ERROR(SR.readBytes(1U, 1U, Buffer));
 }
 
 // Tests that a read which outputs into a full destination buffer works and