[PATCH] D51547: MachO: Fix out-of-bounds memory access in getString16

[Tom Stellard via Phabricator via llvm-commits]

tstellar created this revision.
tstellar added reviewers: lhames, kledzik.
Herald added a reviewer: javed.absar.
Herald added a subscriber: kristof.beyls.

This fixes the following tests when gcc is compiled with gcc8:

lld :: mach-o/do-not-emit-unwind-fde-arm64.yaml
lld :: mach-o/eh-frame-relocs-arm64.yaml

llvm.org/PR38096


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D51547

Files:
  lib/ReaderWriter/MachO/MachONormalizedFileBinaryUtils.h


Index: lib/ReaderWriter/MachO/MachONormalizedFileBinaryUtils.h
===================================================================
--- lib/ReaderWriter/MachO/MachONormalizedFileBinaryUtils.h
+++ lib/ReaderWriter/MachO/MachONormalizedFileBinaryUtils.h
@@ -185,12 +185,11 @@
   return result;
 }
 
-inline StringRef getString16(const char s[16]) {
-  StringRef x = s;
-  if ( x.size() > 16 )
-    return x.substr(0, 16);
-  else
-    return x;
+static StringRef getString16(const char s[16]) {
+  // The StringRef(const char *) constructor passes the const char * to
+  // strlen(), so we can't use this constructor here, because if there is no
+  // null terminator in s, then strlen() will read past the end of the array.
+  return StringRef(s, strnlen(s, 16));
 }
 
 inline void setString16(StringRef str, char s[16]) {


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