Issue #21996 has been updated by luke-gru (Luke Gruber). I just marked this for requiring a backport on Ruby 4.0. We are seeing crashes in production related to this bug on Ruby 4.0.4. Here's the [PR](https://github.com/ruby/ruby/pull/17264). ---------------------------------------- Bug #21996: Crash when modifying instance variables during inspect or Marshal dump https://bugs.ruby-lang.org/issues/21996#change-117531 * Author: jhawthorn (John Hawthorn) * Status: Closed * Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: REQUIRED ---------------------------------------- In #15968 describes an issue where instance variables being modified lead to incorrect Marshal output being generated, which was partially solved by checking for the number of IVs changing and raising an exception. However, if enough IVs removed this could cause the buffer to be moved/re-embedded, but we'd still attempt to read the now removed variables. I've found this reproduces back to Ruby 3.3, but suspect there are other ways to hit issues on older versions. We've seen the test from #15968 start failing on CI recently (likely because the changes to size pools makes this crash reproducible) https://github.com/ruby/ruby/actions/runs/24247666394/job/70803324392 ``` ruby class Evil def initialize(parent) @parent = parent end def marshal_dump @parent.instance_variables.each { |v| @parent.remove_instance_variable(v) } {} end def marshal_load(data) = nil end obj = Object.new obj.instance_variable_set(:@evil, Evil.new(obj)) 10.times { |i| obj.instance_variable_set(:"@v#{i}", 0) } Marshal.dump(obj) # SEGV ``` ``` ruby class Evil def initialize(parent) @parent = parent end def inspect @parent.instance_variables.each { |v| @parent.remove_instance_variable(v) } "" end end obj = Object.new obj.instance_variable_set(:@evil, Evil.new(obj)) 10.times { |i| obj.instance_variable_set(:"@v#{i}", 0) } obj.inspect # SEGV ``` -- https://bugs.ruby-lang.org/