Bug #18084: `JSON.dump` can crash VM.

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN

[ioquatix (Samuel Williams)]

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?

[ioquatix (Samuel Williams)]

• Description updated (diff)

Minor improvement to formatting.

[mame (Yusuke Endoh)]

• Related to Bug #5808: "a = []; a << a; puts JSON.dump(a)" aborted added

[ioquatix (Samuel Williams)]

@nobu (Nobuyoshi Nakada) suggested the following code could be updated:

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

we could also do this on Linux?

[nobu (Nobuyoshi Nakada)]

https://github.com/ruby/ruby/pull/4751

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|574f3af36ea008896419d2e2407f8fce83bdcd2e.

---

Rewind execution tags more at stack overflow [Bug #18084]