[DebugInfo] Fix infinite loop caused by reading past debug_line end

If the claimed unit length of a debug line program is such that the line
table would finish past the end of the .debug_line section, an infinite
loop occurs because the data extractor will continue to "read" zeroes
without changing the offset. This previously didn't hit an error because
the line table program handles a series of zeroes as a bad extended
opcode.

This patch fixes the inifinite loop and adds a warning if the program
doesn't fit in the available data.

Reviewed by: JDevlieghere

Differential Revision: https://reviews.llvm.org/D72279

2 files changed, 46 insertions, 2 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
index 93b60f1e504..8e7ce58957d 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -528,8 +528,23 @@ Error DWARFDebugLine::LineTable::parse(
   if (PrologueErr)
     return PrologueErr;
 
-  const uint64_t EndOffset =
-      DebugLineOffset + Prologue.TotalLength + Prologue.sizeofTotalLength();
+  uint64_t ProgramLength = Prologue.TotalLength + Prologue.sizeofTotalLength();
+  if (!DebugLineData.isValidOffsetForDataOfSize(DebugLineOffset,
+                                                ProgramLength)) {
+    assert(DebugLineData.size() > DebugLineOffset &&
+           "prologue parsing should handle invalid offset");
+    uint64_t BytesRemaining = DebugLineData.size() - DebugLineOffset;
+    RecoverableErrorCallback(
+        createStringError(errc::invalid_argument,
+                          "line table program with offset 0x%8.8" PRIx64
+                          " has length 0x%8.8" PRIx64 " but only 0x%8.8" PRIx64
+                          " bytes are available",
+                          DebugLineOffset, ProgramLength, BytesRemaining));
+    // Continue by capping the length at the number of remaining bytes.
+    ProgramLength = BytesRemaining;
+  }
+
+  const uint64_t EndOffset = DebugLineOffset + ProgramLength;
 
   // See if we should tell the data extractor the address size.
   if (DebugLineData.getAddressSize() == 0)
diff --git a/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp b/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
index b38e8dfcacc..f29709442d4 100644
--- a/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
+++ b/llvm/unittests/DebugInfo/DWARF/DWARFDebugLineTest.cpp
@@ -438,6 +438,35 @@ TEST_F(DebugLineBasicFixture, ErrorForInvalidExtendedOpcodeLength) {
       "0x00000030 expected 0x02 found 0x01");
 }
 
+TEST_F(DebugLineBasicFixture, ErrorForUnitLengthTooLarge) {
+  if (!setupGenerator())
+    return;
+
+  LineTable &Padding = Gen->addLineTable();
+  // Add some padding to show that a non-zero offset is handled correctly.
+  Padding.setCustomPrologue({{0, LineTable::Byte}});
+  LineTable &LT = Gen->addLineTable();
+  LT.addStandardOpcode(DW_LNS_copy, {});
+  LT.addStandardOpcode(DW_LNS_const_add_pc, {});
+  LT.addExtendedOpcode(1, DW_LNE_end_sequence, {});
+  DWARFDebugLine::Prologue Prologue = LT.createBasicPrologue();
+  // Set the total length to 1 higher than the actual length. The program body
+  // has size 5.
+  Prologue.TotalLength += 6;
+  LT.setPrologue(Prologue);
+
+  generate();
+
+  auto ExpectedLineTable = Line.getOrParseLineTable(LineData, 1, *Context,
+                                                    nullptr, RecordRecoverable);
+  checkError("line table program with offset 0x00000001 has length 0x00000034 "
+             "but only 0x00000033 bytes are available",
+             std::move(Recoverable));
+  ASSERT_THAT_EXPECTED(ExpectedLineTable, Succeeded());
+  EXPECT_EQ((*ExpectedLineTable)->Rows.size(), 2u);
+  EXPECT_EQ((*ExpectedLineTable)->Sequences.size(), 1u);
+}
+
 TEST_F(DebugLineBasicFixture, ErrorForMismatchedAddressSize) {
   if (!setupGenerator())
     return;