Bug #21170: Corrupted Hash (bad VALUE and missing entry) when -1 returned from .hash

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.1: DONTNEED, 3.2: DONE, 3.3: DONE, 3.4: DONE

[jhawthorn (John Hawthorn)]

class MyObj
  attr_reader :hash
  def initialize(val) = @hash = val
end

values = 0.downto(-16).to_a
hash = {}
values.each do |val|
  hash[MyObj.new(val)] = val
end
p hash.values
# => [0, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12, -13, -14, -15, false, -16]

---

st_table reserves -1 as a special hash value to indicate that an entry has been deleted. So that that's a valid value to be returned from the hash function, do_hash replaces -1 with 0 so that it is not mistaken for the sentinel.

Previously, when upgrading an AR table to an ST table, rb_st_add_direct_with_hash was used which did not perform the same conversion, this could lead to a hash in a broken state where one if its entries which was supposed to exist being marked as a tombstone.

The hash could then become further corrupted when the ST table required resizing as the falsely tombstoned entry would be skipped but it would be counted in num entries, leading to an uninitialized entry at index 15.

https://github.com/ruby/ruby/pull/12852

[alanwu (Alan Wu)]

• Backport changed from 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN to 3.1: DONTNEED, 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED

Started with the 3.2 series.

[jhawthorn (John Hawthorn)]

Fixed in 443e2ec27db89c896bd62994f6e04d8d6d48cddb

Backports:
3.2: https://github.com/ruby/ruby/pull/12860
3.3: https://github.com/ruby/ruby/pull/12861
3.4: https://github.com/ruby/ruby/pull/12862

[alanwu (Alan Wu)]

• Status changed from Open to Closed

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 3.1: DONTNEED, 3.2: REQUIRED, 3.3: REQUIRED, 3.4: REQUIRED to 3.1: DONTNEED, 3.2: REQUIRED, 3.3: DONE, 3.4: REQUIRED

Merged into ruby_3_3 at ecb9f7ef372c70c3e4fa81a5002533814a94aa86

[hsbt (Hiroshi SHIBATA)]

• Backport changed from 3.1: DONTNEED, 3.2: REQUIRED, 3.3: DONE, 3.4: REQUIRED to 3.1: DONTNEED, 3.2: DONE, 3.3: DONE, 3.4: REQUIRED

Merged ruby_3_2 at 5e69c1a96264f827eaa611d317c3dab0497f084a

[tenderlovemaking (Aaron Patterson)]

• Backport changed from 3.1: DONTNEED, 3.2: DONE, 3.3: DONE, 3.4: REQUIRED to 3.1: DONTNEED, 3.2: DONE, 3.3: DONE, 3.4: DONE

Backported in 698741d73a0e6c998fb47297ce7b129366b4835b