[ruby-core:105339] [Ruby master Bug#17756] StringScanner#charpos makes segmentation fault when target.byteslice returns non string value

Issue #17756 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.6: UNKNOWN, 2.7: REQUIRED, 3.0: REQUIRED to 2.6: UNKNOWN, 2.7: REQUIRED, 3.0: DONE

ruby_3_0 7b55ff21b52e818819b698326f80158643175645 merged revision(s) 564ccd095a9d7fbe869031dbf666d61dadfdcb03.

----------------------------------------
Bug #17756: StringScanner#charpos makes segmentation fault when target.byteslice returns non string value
https://bugs.ruby-lang.org/issues/17756#change-93753

* Author: kachick (Kenichi Kamiya)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin20]
* Backport: 2.6: UNKNOWN, 2.7: REQUIRED, 3.0: DONE
----------------------------------------
GH-PR: https://github.com/ruby/strscan/pull/20

This is a `strscan` issue.
I'm not sure the best way of how to handle bundled libraries tickets since they are Gemfied.
So I created this ticket just in case.

---

This code makes segmentation fault.

```console
$ ruby -v
ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin20]
```

```ruby
require 'strscan'
string = 'ruby'
scnanner = StringScanner.new(string)
pre = Module.new do
  def byteslice(*args)
  end
end
string.singleton_class.prepend(pre)
scnanner.charpos
```

---Files--------------------------------
ruby_2021-03-28-031219_kamiyakenichinoMacBook-puro.crash (31.3 KB)


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