Issue #21438 has been updated by byroot (Jean Boussier). Status changed from Closed to Open Reopening because the fix we merged need some more work: ``` ruby(rb_vm_bugreport) ../src/vm_dump.c:1175 ruby(rb_bug_for_fatal_signal+0xf5) [0x55800a5c2d45] ../src/error.c:1130 ruby(sigsegv+0x46) [0x55800a31d176] ../src/signal.c:934 ruby(RVALUE_WB_UNPROTECTED+0x14) [0x55800a20e3cd] ../src/gc/default/default.c:1195 ruby(rgengc_check_relation) ../src/gc/default/default.c:4300 ruby(RVALUE_MARKED+0x0) [0x55800a217f31] ../src/gc/default/default.c:4369 ruby(gc_mark_set) ../src/gc/default/default.c:4311 ruby(gc_mark) ../src/gc/default/default.c:4370 ruby(rb_mark_generic_ivar+0xa8) [0x55800a397828] ../src/variable.c:1249 ruby(rb_gc_mark_children+0x108) [0x55800a218618] ../src/gc.c:3145 ruby(gc_mark_stacked_objects+0x76) [0x55800a21c58e] ../src/gc/default/default.c:4563 ruby(gc_mark_stacked_objects_all) ../src/gc/default/default.c:4622 ruby(gc_marks_rest) ../src/gc/default/default.c:5639 ruby(gc_marks+0x55a) [0x55800a220ff2] ../src/gc/default/default.c:5753 ruby(gc_start) ../src/gc/default/default.c:6425 ruby(rb_multi_ractor_p+0x0) [0x55800a222569] ../src/gc/default/default.c:6307 ruby(rb_vm_lock_leave) ../src/vm_sync.h:101 ruby(rb_gc_vm_unlock) ../src/gc.c:144 ruby(garbage_collect) ../src/gc/default/default.c:6309 ruby(objspace_malloc_gc_stress+0x2a) [0x55800a223dce] ../src/gc/default/default.c:7930 ruby(rb_gc_impl_malloc) ../src/gc/default/default.c:7921 ruby(handle_malloc_failure+0x0) [0x55800a224313] ../src/gc.c:5231 ruby(ruby_xmalloc) ../src/gc.c:5221 ruby(get_allocated_entries+0x0) [0x55800a328af2] ../src/st.c:551 ruby(rb_st_init_existing_table_with_size) ../src/st.c:559 ruby(rebuild_table+0xb6) [0x55800a328c46] ../src/st.c:585 ruby(rebuild_table_if_necessary+0x8) [0x55800a3298b0] ../src/st.c:1125 ruby(rb_st_insert) ../src/st.c:1143 ruby(generic_ivar_set_shape_fields+0x228) [0x55800a39ac38] ../src/variable.c:1846 ruby(general_ivar_set+0x17f) [0x55800a39306f] ../src/variable.c:1760 ruby(generic_ivar_set+0x0) [0x55800a39f02d] ../src/variable.c:1909 ruby(ivar_set) ../src/variable.c:2094 ruby(rb_ivar_set) ../src/variable.c:2103 ``` https://github.com/ruby/ruby/actions/runs/15663763782/job/44125172775#step:1... ---------------------------------------- Bug #21438: use-after-free when resizing exivars https://bugs.ruby-lang.org/issues/21438#change-113768 * Author: byroot (Jean Boussier) * Status: Open * Backport: 3.2: WONTFIX, 3.3: REQUIRED, 3.4: REQUIRED ---------------------------------------- Here's a semi-reliable reproduction: ```ruby objs = 10_000.times.map do a = [] a.instance_variable_set(:@a, 1) a end GC.stress = true GC.auto_compact = true steps = 1000.times.map do a = [] a.instance_variable_set(:@a, 1) a.instance_variable_set(:@b, 2) a.instance_variable_set(:@c, 3) a.instance_variable_set(:@d, 4) a.instance_variable_set(:@e, 5) a.instance_variable_set(:@f, 6) a.instance_variable_set(:@g, 7) a.instance_variable_set(:@h, 8) # resize a.instance_variable_set(:@i, 9) a.instance_variable_set(:@j, 10) a end objs.clear GC.stress = false GC.auto_compact = false ``` The Exivar codepath uses `st_update` and allocate within the codebase. If GC trigger, it may remove entires from the table, or delete+insert in case of compaction, and this can trigger a table rebuild of the generic fields st_table in the middle of calling the st_update callback. This can cause entries to be reallocated or rearranged and the update to be for the wrong entry. Auto compaction isn't strictly required to trigger the bug, but makes it more likely. -- https://bugs.ruby-lang.org/