Issue #20691 has been updated by peterzhu2118 (Peter Zhu). I opened a backport PR to 3.3: https://github.com/ruby/ruby/pull/11443 ---------------------------------------- Bug #20691: Use-after-free in WeakKeyMap#clear https://bugs.ruby-lang.org/issues/20691#change-109506 * Author: peterzhu2118 (Peter Zhu) * Status: Open * Backport: 3.1: DONTNEED, 3.2: DONTNEED, 3.3: REQUIRED ---------------------------------------- GitHub PR: https://github.com/ruby/ruby/pull/11437 If the WeakKeyMap has been marked but sweeping hasn't started yet and we cann WeakKeyMap#clear, then there could be a use-after-free because we do not call rb_gc_remove_weak to remove the key from the GC. For example, the following code triggers use-after-free errors in Valgrind: ```ruby map = ObjectSpace::WeakKeyMap.new 1_000.times do 1_000.times do map[Object.new] = nil end map.clear end ``` Output from Valgrind: ``` ==61230== Invalid read of size 8 ==61230== at 0x25CAF8: gc_update_weak_references (default.c:5593) ==61230== by 0x25CAF8: gc_marks_finish (default.c:5641) ==61230== by 0x26031C: gc_marks_continue (default.c:5987) ==61230== by 0x26031C: gc_continue (default.c:2255) ==61230== by 0x2605FC: newobj_cache_miss (default.c:2589) ==61230== by 0x26111F: newobj_alloc (default.c:2622) ==61230== by 0x26111F: rb_gc_impl_new_obj (default.c:2701) ==61230== by 0x26111F: newobj_of (gc.c:890) ==61230== by 0x26111F: rb_wb_protected_newobj_of (gc.c:917) ==61230== by 0x2DE218: rb_class_allocate_instance (object.c:131) ==61230== by 0x2E32A8: class_call_alloc_func (object.c:2141) ==61230== by 0x2E32A8: rb_class_alloc (object.c:2113) ==61230== by 0x2E32A8: rb_class_new_instance_pass_kw (object.c:2172) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ==61230== Address 0x2159cb00 is 0 bytes inside a block of size 8 free'd ==61230== at 0x4849B2C: free (vg_replace_malloc.c:989) ==61230== by 0x248EF1: rb_gc_impl_free (default.c:8512) ==61230== by 0x248EF1: rb_gc_impl_free (default.c:8493) ==61230== by 0x248EF1: ruby_sized_xfree.constprop.0 (gc.c:4178) ==61230== by 0x4627EC: wkmap_free_table_i (weakmap.c:652) ==61230== by 0x3A54AF: apply_functor (st.c:1633) ==61230== by 0x3A54AF: st_general_foreach (st.c:1543) ==61230== by 0x3A54AF: rb_st_foreach (st.c:1640) ==61230== by 0x46203C: wkmap_clear (weakmap.c:973) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ==61230== Block was alloc'd at ==61230== at 0x484680F: malloc (vg_replace_malloc.c:446) ==61230== by 0x25C68E: rb_gc_impl_malloc (default.c:8527) ==61230== by 0x4622E9: wkmap_aset_replace (weakmap.c:817) ==61230== by 0x3A4D02: rb_st_update (st.c:1487) ==61230== by 0x4623E4: wkmap_aset (weakmap.c:854) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ==61230== ==61230== Invalid write of size 8 ==61230== at 0x25CB3B: gc_update_weak_references (default.c:5598) ==61230== by 0x25CB3B: gc_marks_finish (default.c:5641) ==61230== by 0x26031C: gc_marks_continue (default.c:5987) ==61230== by 0x26031C: gc_continue (default.c:2255) ==61230== by 0x2605FC: newobj_cache_miss (default.c:2589) ==61230== by 0x26111F: newobj_alloc (default.c:2622) ==61230== by 0x26111F: rb_gc_impl_new_obj (default.c:2701) ==61230== by 0x26111F: newobj_of (gc.c:890) ==61230== by 0x26111F: rb_wb_protected_newobj_of (gc.c:917) ==61230== by 0x2DE218: rb_class_allocate_instance (object.c:131) ==61230== by 0x2E32A8: class_call_alloc_func (object.c:2141) ==61230== by 0x2E32A8: rb_class_alloc (object.c:2113) ==61230== by 0x2E32A8: rb_class_new_instance_pass_kw (object.c:2172) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ==61230== Address 0x2159cb00 is 0 bytes inside a block of size 8 free'd ==61230== at 0x4849B2C: free (vg_replace_malloc.c:989) ==61230== by 0x248EF1: rb_gc_impl_free (default.c:8512) ==61230== by 0x248EF1: rb_gc_impl_free (default.c:8493) ==61230== by 0x248EF1: ruby_sized_xfree.constprop.0 (gc.c:4178) ==61230== by 0x4627EC: wkmap_free_table_i (weakmap.c:652) ==61230== by 0x3A54AF: apply_functor (st.c:1633) ==61230== by 0x3A54AF: st_general_foreach (st.c:1543) ==61230== by 0x3A54AF: rb_st_foreach (st.c:1640) ==61230== by 0x46203C: wkmap_clear (weakmap.c:973) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ==61230== Block was alloc'd at ==61230== at 0x484680F: malloc (vg_replace_malloc.c:446) ==61230== by 0x25C68E: rb_gc_impl_malloc (default.c:8527) ==61230== by 0x4622E9: wkmap_aset_replace (weakmap.c:817) ==61230== by 0x3A4D02: rb_st_update (st.c:1487) ==61230== by 0x4623E4: wkmap_aset (weakmap.c:854) ==61230== by 0x4296BC: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3788) ==61230== by 0x44A9CD: vm_sendish (vm_insnhelper.c:5955) ==61230== by 0x44A9CD: vm_exec_core (insns.def:898) ==61230== by 0x43A0E4: rb_vm_exec (vm.c:2564) ==61230== by 0x2341B4: rb_ec_exec_node (eval.c:281) ==61230== by 0x236258: ruby_run_node (eval.c:319) ==61230== by 0x15D665: rb_main (main.c:43) ==61230== by 0x15D665: main (main.c:62) ``` -- https://bugs.ruby-lang.org/