[all-commits] [llvm/llvm-project] 1f3def: Fix heap-use-after-free when clearing DIEs in fiss...

[Jordan Rupprecht via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1f3def30ca86a35a173cb1fe10e3e73d2a0d0f6f
      https://github.com/llvm/llvm-project/commit/1f3def30ca86a35a173cb1fe10e3e73d2a0d0f6f
  Author: Jordan Rupprecht <rupprecht at google.com>
  Date:   2022-09-14 (Wed, 14 Sep 2022)

  Changed paths:
    M lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

  Log Message:
  -----------
  Fix heap-use-after-free when clearing DIEs in fission compile units.

D131437 caused heap-use-after-free failures when testing TestCreateAfterAttach.py in asan mode, and "regular" crashes outside of asan.

This appears to be due to a mismatch in a couple places where we choose to clear the DIEs. When we clear the DIE of a skeleton unit, we unconditionally clear the DIE of the DWO unit if it exists. However, `~ScopedExtractDIEs()` only looks at the skeleton unit when deciding to clear. If we decide to clear the skeleton unit because it is now unused, we end up clearing the DWO unit that _is_ used. This change adds a guard by checking `m_cancel_scopes` to prevent clearing the DWO unit.

This is 100% reproducible by running TestCreateAfterAttach.py in asan mode, although it only seems to reproduce in our internal build, so no test case is added here. If someone has suggestions on how to write one, I can add it.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D133790