Bug #20752: IO::Buffer#slice creates mutable IO::Buffer instance that points to readonly memory (e.g. fronzen String)

• Status: Closed
• Assignee: ioquatix (Samuel Williams)
• Target version: -
• ruby -v: ruby 3.4.0dev (2024-09-18T02:16:22Z master 4797b0704a) +PRISM [x86_64-linux]
• Backport: 3.1: REQUIRED, 3.2: DONE, 3.3: REQUIRED

[hanazuki (Kasumi Hanazuki)]

irb(main):001> RUBY_DESCRIPTION.frozen?
=> true
irb(main):002> IO::Buffer.for(RUBY_DESCRIPTION).set_string('perl', 0, 4)
(irb):2:in 'IO::Buffer#set_string': Buffer is not writable! (IO::Buffer::AccessError)
        from (irb):2:in '<main>'
        from <internal:kernel>:191:in 'Kernel#loop'
        from -e:1:in '<main>'
irb(main):003> IO::Buffer.for(RUBY_DESCRIPTION).slice.set_string('perl', 0, 4)
=> 4
irb(main):004> RUBY_DESCRIPTION
=> "perl 3.4.0dev (2024-09-18T02:16:22Z master 4797b0704a) +PRISM [x86_64-linux]"

irb(main):001> IO::Buffer.for(NameError.name).slice.set_string('X', 0, 1)
=> 1
irb(main):002> NameError
(irb):2:in '<main>': uninitialized constant NameError (XameError)
        from <internal:kernel>:191:in 'Kernel#loop'
        from -e:1:in '<main>'

[nobu (Nobuyoshi Nakada)]

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

It results in bus errors with 3.1 and 3.2.

$ ruby3.2 -e 'IO::Buffer.for(RUBY_DESCRIPTION).slice.set_string("perl", 0, 4)'
-e:1: [BUG] Bus Error at 0x0000000100f08b18
ruby 3.2.5 (2024-07-26 revision 31d0f1a2e7) [arm64-darwin23]

$ ruby3.1 -e 'IO::Buffer.for(RUBY_DESCRIPTION).slice(0, 8).set_string("perl", 0, 4)'
-e:1: [BUG] Bus Error at 0x00000001039c7e38
ruby 3.1.4p223 (2023-03-30 revision 957bb7cb81) [arm64-darwin23]

[hanazuki (Kasumi Hanazuki)]

• Subject changed from IO::Buffer#slice fails to copy readonly flag, allowing writes into frozen String to IO::Buffer#slice creates mutable IO::Buffer instance that points to readonly memory (e.g. fronzen String)

[mame (Yusuke Endoh)]

• Assignee set to ioquatix (Samuel Williams)

[ioquatix (Samuel Williams)]

The second example XameError is hilarious, what a great bug. Yes, this should be fixed.

[ioquatix (Samuel Williams)]

Looks like @nobu (Nobuyoshi Nakada) already made a PR here: https://github.com/ruby/ruby/pull/11735

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

[nagachika (Tomoyuki Chikanaga)]

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

ruby_3_2 commit:5777fe5ab57d6479326bdb21ef9a6b88ea1516dc merged revision(s) 637067440f74043c6d79fc649ab8acf1afea25a5.