[llvm] [MachO] Improve bounds check (PR #141083)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-binary-utilities

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

The current check may fail if the addition overflows. I've observed failures of macho-invalid.test on 32-bit due to this.

Instead, compare against the remaining bytes until the end of the object.

---
Full diff: https://github.com/llvm/llvm-project/pull/141083.diff


1 Files Affected:

- (modified) llvm/lib/Object/MachOObjectFile.cpp (+2-1) 


``````````diff
diff --git a/llvm/lib/Object/MachOObjectFile.cpp b/llvm/lib/Object/MachOObjectFile.cpp
index 69d36e6a77db7..5db264207ffb7 100644
--- a/llvm/lib/Object/MachOObjectFile.cpp
+++ b/llvm/lib/Object/MachOObjectFile.cpp
@@ -192,7 +192,8 @@ static Expected<MachOObjectFile::LoadCommandInfo>
 getLoadCommandInfo(const MachOObjectFile &Obj, const char *Ptr,
                    uint32_t LoadCommandIndex) {
   if (auto CmdOrErr = getStructOrErr<MachO::load_command>(Obj, Ptr)) {
-    if (CmdOrErr->cmdsize + Ptr > Obj.getData().end())
+    assert(Ptr <= Obj.getData().end() && "Start must be before end");
+    if (CmdOrErr->cmdsize > (uintptr_t)(Obj.getData().end() - Ptr))
       return malformedError("load command " + Twine(LoadCommandIndex) +
                             " extends past end of file");
     if (CmdOrErr->cmdsize < 8)

``````````

</details>


https://github.com/llvm/llvm-project/pull/141083