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-ASN: AS4713 221.184.0.0/13 X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS 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 061681F463 for ; Thu, 19 Sep 2019 20:32:00 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id EB704120A59; Fri, 20 Sep 2019 05:31:49 +0900 (JST) Received: from o1678948x4.outbound-mail.sendgrid.net (o1678948x4.outbound-mail.sendgrid.net [167.89.48.4]) by neon.ruby-lang.org (Postfix) with ESMTPS id CB70F120A3E for ; Fri, 20 Sep 2019 05:31:47 +0900 (JST) Received: by filter0035p3iad2.sendgrid.net with SMTP id filter0035p3iad2-18447-5D83E5B4-7A 2019-09-19 20:31:48.949750152 +0000 UTC m=+11239.362902830 Received: from herokuapp.com (unknown [54.82.13.197]) by ismtpd0065p1mdw1.sendgrid.net (SG) with ESMTP id ZwCuwxHKQSiC_BUMAA-nKg for ; Thu, 19 Sep 2019 20:31:48.815 +0000 (UTC) Date: Thu, 19 Sep 2019 20:31:49 +0000 (UTC) From: XrXr@users.noreply.github.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 70548 X-Redmine-Project: ruby-trunk X-Redmine-Issue-Id: 16151 X-Redmine-Issue-Author: alanwu X-Redmine-Sender: alanwu 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?PWg67P6owy8ojUUZg1G=2FQM4Z0jTQ2XLCqLM8Y2L8tUvRFuUPM6+aKANjRFY5CJ?= =?us-ascii?Q?rIJGmmPxNQrYh=2Fw0aICxoTTRE0nPbFe0paL46kZ?= =?us-ascii?Q?PHag6B3pg5Oxp00Wv528f0bMplzgeI6TwntDjwX?= =?us-ascii?Q?iNi5en9B82p4FsEO+ctEIPBzK0f7tn9DIJg0ENN?= =?us-ascii?Q?O=2FpaWQ0HBnv8FDwmUxxL38Hg4Jox2C+2hSw=3D=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 94993 Subject: [ruby-core:94993] [Ruby master Bug#16151] [PATCH] Fix a class of fstring related use-after-free 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 #16151 has been updated by alanwu (Alan Wu). @mame I think that class is used frequently, though I'm not sure if Rails tries to deduplicate instances with fstrings. Regardless, it seems that removing buffer deduplication all together isn't very workable, since we need to backport it, even if it's acceptable in a version that doesn't track taint. I think refusing to do buffer deduplicate on frozen strings seems promising. I will try to get some statistics on how many strings it ends up refusing. ---------------------------------------- Bug #16151: [PATCH] Fix a class of fstring related use-after-free https://bugs.ruby-lang.org/issues/16151#change-81621 * Author: alanwu (Alan Wu) * Status: Open * Priority: Normal * Assignee: * Target version: * ruby -v: ruby 2.7.0dev (2019-09-07T18:26:35Z master e9bc8b35c6) [x86_64-linux] * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN ---------------------------------------- Pull request: https://github.com/ruby/ruby/pull/2435 ## The bug Run the following against master(e9bc8b3) to observe use-after-free: ```ruby -('a' * 30).force_encoding(Encoding::ASCII) a = ('a' * 30).force_encoding(Encoding::ASCII).taint t = Thread.new{} t.name = a eval('', binding, t.name) p a ``` ```ruby -('a' * 30).force_encoding(Encoding::ASCII) a = ('a' * 30).force_encoding(Encoding::ASCII).taint require 'ripper' ripper = Ripper.new("", a) eval('', binding, ripper.filename) p a ``` There may be other cases in the standard library or in the wild. ## Background When a string has both `STR_NOEMBED` and `STR_SHARED` set, it relies on a different string for its buffer. I will refer to strings that are depended upon as "shared roots". Shared roots are frozen and have the `STR_SHARED` unset. This is a bit unintuitive to me. A name for `STR_SHARED` that makes more sense to me would be `STR_BUFFER_ELSEWHERE`. ## What went wrong It is not safe to free the buffer of a shared root while it has dependants. The root and its dependants use the same buffer. As such, it is only safe to free the shared buffer when all users are unreachable on the heap. ## The Fix `rb_fstring` has a code path that frees and replaces the buffer of its input. Using this code path on the shared root of dependant strings sets up use-after-free. This patch removes the problematic code path as no tests require said buffer replacement functionality. Additionally, there has been three other issues that steam from this particular code path. See #15926, #15916 and #16136 --- I used @mame's commit in #16136 as the starting point for this investigation. Thank you! -- https://bugs.ruby-lang.org/