From cd63a636640c38d530aaa12476fc03ab7372f6a9 Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel@labath.sk>
Date: Mon, 24 Jun 2019 09:11:24 +0000
Subject: [PATCH] [Support] Fix error handling in DataExtractor::get[US]LEB128

Summary:
These functions are documented as not modifying the offset argument if
the extraction fails (just like other DataExtractor functions). However,
while reviewing D63591 we discovered that this is not the case -- if the
function reaches the end of the data buffer, it will just return the
value parsed until that point and set offset to point to the end of the
buffer.

This fixes the functions to act as advertised, and adds a regression
test.

Reviewers: dblaikie, probinson, bkramer

Subscribers: kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63645

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364169 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Support/DataExtractor.cpp           | 28 ++++++++++++-------------
 unittests/Support/DataExtractorTest.cpp | 10 +++++++++
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/lib/Support/DataExtractor.cpp b/lib/Support/DataExtractor.cpp
index 6328d779b3d..18e1423b546 100644
--- a/lib/Support/DataExtractor.cpp
+++ b/lib/Support/DataExtractor.cpp
@@ -157,12 +157,12 @@ uint64_t DataExtractor::getULEB128(uint32_t *offset_ptr) const {
     byte = Data[offset++];
     result |= uint64_t(byte & 0x7f) << shift;
     shift += 7;
-    if ((byte & 0x80) == 0)
-      break;
+    if ((byte & 0x80) == 0) {
+      *offset_ptr = offset;
+      return result;
+    }
   }
-
-  *offset_ptr = offset;
-  return result;
+  return 0;
 }
 
 int64_t DataExtractor::getSLEB128(uint32_t *offset_ptr) const {
@@ -178,14 +178,14 @@ int64_t DataExtractor::getSLEB128(uint32_t *offset_ptr) const {
     byte = Data[offset++];
     result |= uint64_t(byte & 0x7f) << shift;
     shift += 7;
-    if ((byte & 0x80) == 0)
-      break;
+    if ((byte & 0x80) == 0) {
+      // Sign bit of byte is 2nd high order bit (0x40)
+      if (shift < 64 && (byte & 0x40))
+        result |= -(1ULL << shift);
+
+      *offset_ptr = offset;
+      return result;
+    }
   }
-
-  // Sign bit of byte is 2nd high order bit (0x40)
-  if (shift < 64 && (byte & 0x40))
-    result |= -(1ULL << shift);
-
-  *offset_ptr = offset;
-  return result;
+  return 0;
 }
diff --git a/unittests/Support/DataExtractorTest.cpp b/unittests/Support/DataExtractorTest.cpp
index 5663dad5cb6..9726a74d81f 100644
--- a/unittests/Support/DataExtractorTest.cpp
+++ b/unittests/Support/DataExtractorTest.cpp
@@ -116,4 +116,14 @@ TEST(DataExtractorTest, LEB128) {
   EXPECT_EQ(8U, offset);
 }
 
+TEST(DataExtractorTest, LEB128_error) {
+  DataExtractor DE(StringRef("\x81"), false, 8);
+  uint32_t Offset = 0;
+  EXPECT_EQ(0U, DE.getULEB128(&Offset));
+  EXPECT_EQ(0U, Offset);
+
+  Offset = 0;
+  EXPECT_EQ(0U, DE.getSLEB128(&Offset));
+  EXPECT_EQ(0U, Offset);
+}
 }