From: "ioquatix (Samuel Williams)" <noreply@...>
Date: 2021-08-18T04:20:37+00:00
Subject: [ruby-core:104965] [Ruby master Bug#18084] `JSON.dump` can crash VM.

Issue #18084 has been updated by ioquatix (Samuel Williams).


@nobu suggested the following code could be updated:

~~~ clang
sigill(int sig SIGINFO_ARG)
{
    check_reserved_signal("ILL");
#if defined __APPLE__
    CHECK_STACK_OVERFLOW();
#endif
~~~

we could also do this on Linux?

----------------------------------------
Bug #18084: `JSON.dump` can crash VM.
https://bugs.ruby-lang.org/issues/18084#change-93329

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
~~~ ruby
require 'json'

x = {}; x[:x] = x

JSON.dump(x) # => nil
JSON.dump(x) # => SIGILL
~~~

Results from our friendly all ruby bot:

~~~
:x: 1.8
-:1:in `require': no such file to load -- json (LoadError)
    from -:1
exit: 1

:x: 1.9
/build-all-ruby/1.9.3-p551/lib/ruby/1.9.1/json/common.rb:216: stack level too deep (SystemStackError)
exit: 1

:x: 2.0
/build-all-ruby/2.0.0-p648/lib/ruby/2.0.0/json/common.rb:224: stack level too deep (SystemStackError)
exit: 1

:x: 2.1
/build-all-ruby/2.1.10/lib/ruby/2.1.0/json/common.rb:223: stack level too deep (SystemStackError)
exit: 1

:x: 2.2
/build-all-ruby/2.2.10/lib/ruby/2.2.0/json/common.rb:223:in `encode': stack level too deep (SystemStackError)
    from /build-all-ruby/2.2.10/lib/ruby/2.2.0/json/common.rb:223:in `generate'
    from /build-all-ruby/2.2.10/lib/ruby/2.2.0/json/common.rb:223:in `generate'
    from /build-all-ruby/2.2.10/lib/ruby/2.2.0/json/common.rb:394:in `dump'
    from -:5:in `<main>'
Show more
exit: 1

:x: 2.3
/build-all-ruby/2.3.8/lib/ruby/2.3.0/json/common.rb:224:in `encode': stack level too deep (SystemStackError)
    from /build-all-ruby/2.3.8/lib/ruby/2.3.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.3.8/lib/ruby/2.3.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.3.8/lib/ruby/2.3.0/json/common.rb:395:in `dump'
    from -:5:in `<main>'
Show more
exit: 1

:x: 2.4
/build-all-ruby/2.4.10/lib/ruby/2.4.0/json/common.rb:224:in `encode': stack level too deep (SystemStackError)
    from /build-all-ruby/2.4.10/lib/ruby/2.4.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.4.10/lib/ruby/2.4.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.4.10/lib/ruby/2.4.0/json/common.rb:394:in `dump'
    from -:5:in `<main>'
Show more
exit: 1

:x: 2.5
/build-all-ruby/2.5.8/lib/ruby/2.5.0/json/common.rb:224:in `generate': stack level too deep (SystemStackError)
    from /build-all-ruby/2.5.8/lib/ruby/2.5.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.5.8/lib/ruby/2.5.0/json/common.rb:394:in `dump'
    from -:5:in `<main>'
exit: 1

:x: 2.6
/build-all-ruby/2.6.6/lib/ruby/2.6.0/json/common.rb:224:in `generate': stack level too deep (SystemStackError)
    from /build-all-ruby/2.6.6/lib/ruby/2.6.0/json/common.rb:224:in `generate'
    from /build-all-ruby/2.6.6/lib/ruby/2.6.0/json/common.rb:394:in `dump'
    from -:5:in `<main>'
exit: 1

:x: 2.7 -- 58bd943436 (2021-08-17T17:25:19Z)
-: machine stack overflow in critical region (fatal)
exit: 1
~~~

So in the best case, we got `SystemStackError`, and from 2.7+ we get a fatal error.

Do we want to improve this behaviour or is this expected, and if so, should we add documentation to this effect?



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