[PATCH] D60202: llvm-undname: Fix a crash-on-invalid

[Nico Weber via Phabricator via llvm-commits]

thakis created this revision.
thakis added a reviewer: zturner.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Found by oss-fuzz, fixes issues 12435 and 12438 on oss-fuzz.


https://reviews.llvm.org/D60202

Files:
  llvm/lib/Demangle/MicrosoftDemangle.cpp
  llvm/test/Demangle/invalid-manglings.test


Index: llvm/test/Demangle/invalid-manglings.test
===================================================================
--- llvm/test/Demangle/invalid-manglings.test
+++ llvm/test/Demangle/invalid-manglings.test
@@ -8,4 +8,9 @@
 ?f0@@YAXPEU?$AS_@$00$$CAD at __clang@@@Z
 ; CHECK-EMPTY:
 ; CHECK-NEXT: ?f0@@YAXPEU?$AS_@$00$$CAD at __clang@@@Z
-; CHECK-NEXT: error: Invalid mangled name
\ No newline at end of file
+; CHECK-NEXT: error: Invalid mangled name
+
+?@@8
+; CHECK-EMPTY:
+; CHECK-NEXT: ?@@8
+; CHECK-NEXT: error: Invalid mangled name
Index: llvm/lib/Demangle/MicrosoftDemangle.cpp
===================================================================
--- llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -1276,12 +1276,16 @@
   return nullptr;
 }
 
+// Returns MangledName's prefix before the first '@', or an error if
+// MangledName contains no '@' or the prefix has length 0.
 StringView Demangler::demangleSimpleString(StringView &MangledName,
                                            bool Memorize) {
   StringView S;
   for (size_t i = 0; i < MangledName.size(); ++i) {
     if (MangledName[i] != '@')
       continue;
+    if (i == 0)
+      break;
     S = MangledName.substr(0, i);
     MangledName = MangledName.dropFront(i + 1);
 


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