From: "Eregon (Benoit Daloze)" <redmine@...>
Date: 2013-04-20T18:39:09+09:00
Subject: [ruby-core:54478] [Backport 200 - Backport #8276] Marshal.load modifies restored object after calling #marshal_load


Issue #8276 has been updated by Eregon (Benoit Daloze).


nobu (Nobuyoshi Nakada) wrote:
> Note that returning frozen object from marshal_load is wrong in common.
> In this particular case, removed excess encoding information because it is duplicated to marshal_dump data, but the other instance variables are set after marshal_load.
> Your code has a potential bug and should separate marshal_dump and initialize.

How would you reliably freeze the object again then?
Should it be a feature of Marshal?
----------------------------------------
Backport #8276: Marshal.load modifies restored object after calling #marshal_load 
https://bugs.ruby-lang.org/issues/8276#change-38781

Author: Eregon (Benoit Daloze)
Status: Assigned
Priority: Normal
Assignee: nagachika (Tomoyuki Chikanaga)
Category: 
Target version: 


Given this code, a simple class freezing instances on creation (so they are immutable):

class T
  def initialize(data)
    @data = data
    freeze
  end

  def marshal_dump
    @data
  end

  def marshal_load data
    initialize(data)
  end
end

t = T.new("dd")
s = Marshal.dump(t)
p Marshal.load(s) # =>  ...:in `load': can't modify frozen T (RuntimeError)


Freezing on creation from Marshal is needed to ensure immutability and it seems the right place to do it.
It used to work (ruby 2.0.0dev (2012-07-15 trunk 36395) [x86_64-darwin10.8.0] did fine).
The backtrace:

(gdb) bt
#0  rb_raise (exc=4304355040, fmt=0x1001be828 "can't modify frozen %s") at error.c:1810
#1  0x000000010004344f in rb_error_frozen (what=<value temporarily unavailable, due to optimizations>) at error.c:2020
#2  0x0000000100004600 in rb_enc_associate_index (obj=<value temporarily unavailable, due to optimizations>, idx=1) at encoding.c:749
#3  0x000000010008233b in r_ivar (obj=4320803800, has_encoding=0x0, arg=0x1006b84b0) at marshal.c:1374
#4  0x00000001000811f1 in r_object0 (arg=0x1006b84b0, ivp=<value temporarily unavailable, due to optimizations>, extmod=8) at marshal.c:1475
#5  0x00000001000821ad in r_object [inlined] () at /Users/benoitdaloze/EREGONMS/Ruby/git/ruby/marshal.c:1890
#6  0x00000001000821ad in marshal_load (argc=<value temporarily unavailable, due to optimizations>, argv=<value temporarily unavailable, due to optimizations>) at marshal.c:1978
...


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