Issue #15792 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Closed

Thank you, fixed at https://git.ruby-lang.org/ruby.git/commit/?id=3D3f95620=
15e651735bfc2fdd14e8f6963b673e22a.

----------------------------------------
Bug #15792: GC can leave strings used as hash keys in a corrupted state
https://bugs.ruby-lang.org/issues/15792#change-77789

* Author: byroot (Jean Boussier)
* Status: Closed
* Priority: Normal
* Assignee: =

* Target version: =

* ruby -v: 2.6.2
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
The following script showcase the issue:

```
#!/usr/bin/env ruby --disable-gems
a =3D ('a' * 24).encode(Encoding::ASCII).gsub('x', '')
b =3D ('b' * 24).encode(Encoding::ASCII).gsub('x', '')

hash =3D {}
hash[a] =3D true
hash[b] =3D true

puts "Bebore garbage_collection: a=3D#{a.inspect} b=3D#{b.inspect}"
4.times { GC.start }
puts "After garbage_collection: a=3D#{a.inspect} b=3D#{b.inspect}"
```

Expected output:

```
Bebore garbage_collection: a=3D"aaaaaaaaaaaaaaaaaaaaaaaa" b=3D"bbbbbbbbbbbb=
bbbbbbbbbbbb"
After garbage_collection: a=3D"aaaaaaaaaaaaaaaaaaaaaaaa" b=3D"bbbbbbbbbbbbb=
bbbbbbbbbbb"
```

Actual output:

```
Ruby: 2.6.2
Bebore garbage_collection: a=3D"aaaaaaaaaaaaaaaaaaaaaaaa" b=3D"bbbbbbbbbbbb=
bbbbbbbbbbbb"
After garbage_collection: a=3D"}\x0Eu\xDB\xFC\a\x00\x80\xE9\ru\xDB\xFC\a\x0=
0\x10\x04\x00aaaaaa" b=3D"\x00\x00\x00\x00\x00\x00\x00\xC0\x00\x00\x00\x00\=
x00\x00\x00\xC0\x02\x00bbbbbb"
```

We reduced the repro script as much as we could, both the `.encode(ASCII)` =
and the `gsub` are necessary for the bug to manifest itself.

We also used `ObjectSpace.dump()` to analyze the corrupted string.

```
b =3D "shared":true, "encoding":"US-ASCII", "references":["0x7faf4a01aeb8"]
0x7faf4a01aeb8 =3D "frozen":true, "fstring":true, "bytesize":24, "value":"b=
bbbbbbbbbbbbbbbbbbbbbbb", "encoding":"US-ASCII"
```

Big thanks to =C9douard Chin who did most of the initial repro reduction.



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