From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id 332771F5AE for ; Wed, 22 Jul 2020 07:42:13 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 756AA120A90; Wed, 22 Jul 2020 16:41:39 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id C2EF9120A8F for ; Wed, 22 Jul 2020 16:41:35 +0900 (JST) Received: by filterdrecv-p3las1-7754f7d4cc-gtvm8 with SMTP id filterdrecv-p3las1-7754f7d4cc-gtvm8-18-5F17EDC5-19 2020-07-22 07:41:57.285903053 +0000 UTC m=+2294898.787787244 Received: from herokuapp.com (unknown) by ismtpd0054p1iad1.sendgrid.net (SG) with ESMTP id 8wRgr_KWSPS6xD41-C7WSg for ; Wed, 22 Jul 2020 07:41:57.109 +0000 (UTC) Date: Wed, 22 Jul 2020 07:41:57 +0000 (UTC) From: hanmac@gmx.de Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 75049 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Bug X-Redmine-Issue-Id: 17023 X-Redmine-Issue-Author: larskanis X-Redmine-Issue-Assignee: tenderlovemaking X-Redmine-Sender: Hanmac X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?z6kUDlxbGclXLcwluHLUb5EO6uh6mW1Jn0ZSGyxj3H3hdmY=2FvZv9Y1YxXE3kCi?= =?us-ascii?Q?PLCn5Vba9y01px+CypNW1EP0c+4apfLEEJXRIrr?= =?us-ascii?Q?gd66kEVynqK+grz=2FqvmQR5VJkcz1NUp083TAnRl?= =?us-ascii?Q?=2FU4Sy+GYOCvJZu2Lff8eu6gvFxuUepbz5xThW8z?= =?us-ascii?Q?GKWMeMUD5nBPK2vZEpZ98NxTc893qPvtbmg=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 99260 Subject: [ruby-core:99260] [Ruby master Bug#17023] How to prevent String memory to be relocated in ruby-ffi X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #17023 has been updated by Hanmac (Hans Mackowiak). the problem there is that ruby can't know how long the C lib is going to use the String. Depending on the C Function, might even take "ownership" of the string and does free it itself, so when Ruby would free the string too, it causes a Double Free crash. ---------------------------------------- Bug #17023: How to prevent String memory to be relocated in ruby-ffi https://bugs.ruby-lang.org/issues/17023#change-86644 * Author: larskanis (Lars Kanis) * Status: Closed * Priority: Normal * Assignee: tenderlovemaking (Aaron Patterson) * ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux] * Backport: 2.5: DONTNEED, 2.6: DONTNEED, 2.7: DONE ---------------------------------------- [ruby-ffi](https://github.com/ffi/ffi) allows to pass String objects to C by using the `:string` argument type. This way the string memory returned by `RSTRING_PTR` is passed to the C function. The user has to ensure on Ruby level that the string isn't GC'ed - as long as it is used on C level. That's the contract and this worked with all past ruby versions, but ruby-2.7 introduced `GC.compact`, which can relocate strings to another memory location. This example shows the situation and that the string is relocated although it is still referenced in ruby code: ```ruby File.write "string-relocate.c", <<-EOC static char *g_str; void set(char* str) { g_str = str; } char* get() { return g_str; } EOC system "gcc -shared -fPIC string-relocate.c -o string-relocate.so" require 'ffi' class Foo extend FFI::Library ffi_lib File.expand_path('string-relocate.so') attach_function :set, [:string], :void attach_function :get, [], :string def initialize(count) proc {} # necessary to trigger relocation a = "a" * count set(a) GC.verify_compaction_references(toward: :empty, double_heap: true) puts "get(#{count}): #{get} (should be: #{a})" end end Foo.new(23) Foo.new(24) ``` The output looks like so on ruby-2.7.1: ``` get(23): (should be: aaaaaaaaaaaaaaaaaaaaaaa) get(24): aaaaaaaaaaaaaaaaaaaaaaaa (should be: aaaaaaaaaaaaaaaaaaaaaaaa) ``` So using `GC.compact` while a string parameter is in use, both on Ruby and on C level, can cause invalid memory access. How can this prevented? A C extension is expected to use `rb_gc_mark()` in order to pin the VALUE to a memory location. But I couldn't find a way to pin a `VALUE` at the time the argument is passed to the C function, which is the only point in time ruby-ffi has access to it. ---Files-------------------------------- string-relocate.rb (653 Bytes) 0001-Only-marked-objects-should-be-considered-movable.patch (1.23 KB) -- https://bugs.ruby-lang.org/