Issue #20688 has been updated by peterzhu2118 (Peter Zhu). I opened a PR to backport to Ruby 3.3: https://github.com/ruby/ruby/pull/11439 ---------------------------------------- Bug #20688: Use-after-free in WeakMap and WeakKeyMap https://bugs.ruby-lang.org/issues/20688#change-109497 * Author: peterzhu2118 (Peter Zhu) * Status: Closed * Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: REQUIRED ---------------------------------------- GitHub PR: https://github.com/ruby/ruby/pull/11421 We cannot free the weakmap_entry before the ST_DELETE because it could hash the key which would read the weakmap_entry and would cause a use-after-free. Instead, we store the entry and free it on the next iteration. For example, the following script triggers a use-after-free in Valgrind: ```ruby weakmap = ObjectSpace::WeakMap.new 10_000.times { weakmap[Object.new] = Object.new } ``` ``` ==25795== Invalid read of size 8 ==25795== at 0x462297: wmap_cmp (weakmap.c:165) ==25795== by 0x3A2B1C: find_table_bin_ind (st.c:930) ==25795== by 0x3A5EAA: st_general_foreach (st.c:1599) ==25795== by 0x3A5EAA: rb_st_foreach (st.c:1640) ==25795== by 0x25C991: gc_mark_children (default.c:4870) ==25795== by 0x25C991: gc_marks_wb_unprotected_objects_plane (default.c:5565) ==25795== by 0x25C991: rgengc_rememberset_mark_plane (default.c:5557) ==25795== by 0x25C991: rgengc_rememberset_mark (default.c:6233) ==25795== by 0x25C991: gc_marks_start (default.c:6057) ==25795== by 0x25C991: gc_marks (default.c:6077) ==25795== by 0x25C991: gc_start (default.c:6723) ==25795== by 0x260F96: heap_prepare (default.c:2282) ==25795== by 0x260F96: heap_next_free_page (default.c:2489) ==25795== by 0x260F96: newobj_cache_miss (default.c:2598) ==25795== by 0x26197F: newobj_alloc (default.c:2622) ==25795== by 0x26197F: rb_gc_impl_new_obj (default.c:2701) ==25795== by 0x26197F: newobj_of (gc.c:890) ==25795== by 0x26197F: rb_wb_protected_newobj_of (gc.c:917) ==25795== by 0x2DEA88: rb_class_allocate_instance (object.c:131) ==25795== by 0x2E3B18: class_call_alloc_func (object.c:2141) ==25795== by 0x2E3B18: rb_class_alloc (object.c:2113) ==25795== by 0x2E3B18: rb_class_new_instance_pass_kw (object.c:2172) ==25795== by 0x429DDC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3786) ==25795== by 0x44B08D: vm_sendish (vm_insnhelper.c:5953) ==25795== by 0x44B08D: vm_exec_core (insns.def:898) ==25795== by 0x43A7A4: rb_vm_exec (vm.c:2564) ==25795== by 0x234914: rb_ec_exec_node (eval.c:281) ==25795== Address 0x21603710 is 0 bytes inside a block of size 16 free'd ==25795== at 0x4849B2C: free (vg_replace_malloc.c:989) ==25795== by 0x249651: rb_gc_impl_free (default.c:8527) ==25795== by 0x249651: rb_gc_impl_free (default.c:8508) ==25795== by 0x249651: ruby_sized_xfree.constprop.0 (gc.c:4178) ==25795== by 0x4626EC: ruby_sized_xfree_inlined (gc.h:277) ==25795== by 0x4626EC: wmap_free_entry (weakmap.c:45) ==25795== by 0x4626EC: wmap_mark_weak_table_i (weakmap.c:61) ==25795== by 0x3A5CEF: apply_functor (st.c:1633) ==25795== by 0x3A5CEF: st_general_foreach (st.c:1543) ==25795== by 0x3A5CEF: rb_st_foreach (st.c:1640) ==25795== by 0x25C991: gc_mark_children (default.c:4870) ==25795== by 0x25C991: gc_marks_wb_unprotected_objects_plane (default.c:5565) ==25795== by 0x25C991: rgengc_rememberset_mark_plane (default.c:5557) ==25795== by 0x25C991: rgengc_rememberset_mark (default.c:6233) ==25795== by 0x25C991: gc_marks_start (default.c:6057) ==25795== by 0x25C991: gc_marks (default.c:6077) ==25795== by 0x25C991: gc_start (default.c:6723) ==25795== by 0x260F96: heap_prepare (default.c:2282) ==25795== by 0x260F96: heap_next_free_page (default.c:2489) ==25795== by 0x260F96: newobj_cache_miss (default.c:2598) ==25795== by 0x26197F: newobj_alloc (default.c:2622) ==25795== by 0x26197F: rb_gc_impl_new_obj (default.c:2701) ==25795== by 0x26197F: newobj_of (gc.c:890) ==25795== by 0x26197F: rb_wb_protected_newobj_of (gc.c:917) ==25795== by 0x2DEA88: rb_class_allocate_instance (object.c:131) ==25795== by 0x2E3B18: class_call_alloc_func (object.c:2141) ==25795== by 0x2E3B18: rb_class_alloc (object.c:2113) ==25795== by 0x2E3B18: rb_class_new_instance_pass_kw (object.c:2172) ==25795== by 0x429DDC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3786) ==25795== by 0x44B08D: vm_sendish (vm_insnhelper.c:5953) ==25795== by 0x44B08D: vm_exec_core (insns.def:898) ==25795== by 0x43A7A4: rb_vm_exec (vm.c:2564) ==25795== Block was alloc'd at ==25795== at 0x484680F: malloc (vg_replace_malloc.c:446) ==25795== by 0x25CE9E: rb_gc_impl_malloc (default.c:8542) ==25795== by 0x462A39: wmap_aset_replace (weakmap.c:423) ==25795== by 0x3A5542: rb_st_update (st.c:1487) ==25795== by 0x462B8E: wmap_aset (weakmap.c:452) ==25795== by 0x429DDC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3786) ==25795== by 0x44B08D: vm_sendish (vm_insnhelper.c:5953) ==25795== by 0x44B08D: vm_exec_core (insns.def:898) ==25795== by 0x43A7A4: rb_vm_exec (vm.c:2564) ==25795== by 0x234914: rb_ec_exec_node (eval.c:281) ==25795== by 0x2369B8: ruby_run_node (eval.c:319) ==25795== by 0x15D675: rb_main (main.c:43) ==25795== by 0x15D675: main (main.c:62) ``` -- https://bugs.ruby-lang.org/