ruby-core

Issue #15792 has been updated by byroot (Jean Boussier).


符ouad Chin bisected the script against the MRI repository, and found https://bugs.ruby-lang.org/issues/15251 the first commit to trigger the problem.

That being said it's unlikely to really be the source of the bug. It's much more likely to be in the `fstring` function.



----------------------------------------
Bug #15792: GC can leave strings used as hash keys in a corrupted state
https://bugs.ruby-lang.org/issues/15792#change-77778

* Author: byroot (Jean Boussier)
* Status: Open
* 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 = ('a' * 24).encode(Encoding::ASCII).gsub('x', '')
b = ('b' * 24).encode(Encoding::ASCII).gsub('x', '')

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

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

Expected output:

```
Bebore garbage_collection: a="aaaaaaaaaaaaaaaaaaaaaaaa" b="bbbbbbbbbbbbbbbbbbbbbbbb"
After garbage_collection: a="aaaaaaaaaaaaaaaaaaaaaaaa" b="bbbbbbbbbbbbbbbbbbbbbbbb"
```

Actual output:

```
Ruby: 2.6.2
Bebore garbage_collection: a="aaaaaaaaaaaaaaaaaaaaaaaa" b="bbbbbbbbbbbbbbbbbbbbbbbb"
After garbage_collection: a="}\x0Eu\xDB\xFC\a\x00\x80\xE9\ru\xDB\xFC\a\x00\x10\x04\x00aaaaaa" b="\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 = "shared":true, "encoding":"US-ASCII", "references":["0x7faf4a01aeb8"]
0x7faf4a01aeb8 = "frozen":true, "fstring":true, "bytesize":24, "value":"bbbbbbbbbbbbbbbbbbbbbbbb", "encoding":"US-ASCII"
```

Big thanks to ノdouard Chin who did most of the initial repro reduction.



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