From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB6E5C001DF for ; Fri, 20 Oct 2023 15:19:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377679AbjJTPT3 (ORCPT ); Fri, 20 Oct 2023 11:19:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59008 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377620AbjJTPT2 (ORCPT ); Fri, 20 Oct 2023 11:19:28 -0400 Received: from mail-pg1-x52a.google.com (mail-pg1-x52a.google.com [IPv6:2607:f8b0:4864:20::52a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 29645D55 for ; Fri, 20 Oct 2023 08:19:26 -0700 (PDT) Received: by mail-pg1-x52a.google.com with SMTP id 41be03b00d2f7-5b852632be4so29793a12.1 for ; Fri, 20 Oct 2023 08:19:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1697815165; x=1698419965; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=yXhmtsd7v35VsKDTvdSZ2foO72l9HxK/7NMvbj357Oc=; b=QEltRJ17lV9C8l8ZncfVwjXjdgfQIWCXoLLpXZfXy2mCRDe8LJjbc0yDWG14/9xwPf g/9CIXVd0tzFiHyWUJZKCwa8FbXgy4nckO0Fg09Lfuf6OGK2QCSA7gOdHZiyOgDHEeHx aANid33mJ/4vQyoxA7IrskLpOsN8MKshHgkRWWrd5tilG6ZAuVAjkM8pVu7h2sCuscdO f16UnCPThQoWcQf8gtYsTq8Z0LOZMik2kiueUZICOzmVOoJXzWWCPpBivEk70YSsS2hn lu7JOjTc4RdYvzoX7wpBlu9B7nkXgcQJWlQ6o0MCi96Fl8sNtMWgXwOOWCyRICyIERId MaTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697815165; x=1698419965; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=yXhmtsd7v35VsKDTvdSZ2foO72l9HxK/7NMvbj357Oc=; b=kk6UnjgyTDNLuO4qn73WiABJ0BIy1VWQRGEzCf35YDGGQygkyjH85DcohZnstAiyh1 kk+yK0thfuUTpfpWAj3lX9er37EMUqTtZ1fVF3DYqssBdNEUslwMoHROXQE+fK8Ly3Sd 9Jl4lLYUq0fs3XalVp3sfiVipUSf+uM1h37GB4RgMTwBJq8lrhi7wkZF2H9Hqo00NzIQ 7giY4GEMKouay1bMnKMAwTlWUVcwdxV46YwTfVepIH8EUtPtX1rIpVcViv4GH5IlufMe x7bD9a5i/F18F7llRpQ7lSKf2D5NITbjkfGK7h6zYSOZtYkrljs+irC3zo5Y61HvokxS CUiQ== X-Gm-Message-State: AOJu0YwhxJWk3Nf2El824sG9OMRGUdIo4KJmDe4wnQ2VAYiVm2uQ+XM3 peb3Gq4BeajqisYg7PnO1X8IOA== X-Google-Smtp-Source: AGHT+IE6s6NkBDf7TGkQ+jf9gxmZjQduI9EXHQyK2mEMbBuoJLYncEiyFKNJSrCv2CwYF2o28pDQRA== X-Received: by 2002:a05:6a21:7881:b0:16e:26fd:7c02 with SMTP id bf1-20020a056a21788100b0016e26fd7c02mr2448569pzc.2.1697815165551; Fri, 20 Oct 2023 08:19:25 -0700 (PDT) Received: from [10.4.4.198] ([139.177.225.251]) by smtp.gmail.com with ESMTPSA id 25-20020a17090a031900b0026b3a86b0d5sm1732974pje.33.2023.10.20.08.19.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Oct 2023 08:19:24 -0700 (PDT) Message-ID: <58a42dfb-38f8-4935-ac4d-4ec34c3c9504@bytedance.com> Date: Fri, 20 Oct 2023 23:19:20 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: KASAN: slab-use-after-free Read in radix_tree_lookup in&after Linux Kernel 6.4-rc6 Content-Language: en-US To: Matthew Wilcox Cc: Petr Mladek , Zhang Zhiyu , linux-kernel@vger.kernel.org, Andrew Morton , secalert@redhat.com References: From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Matthew, On 2023/10/20 22:58, Matthew Wilcox wrote: > On Fri, Oct 20, 2023 at 09:51:18PM +0800, Qi Zheng wrote: >> Hi all, >> >> On 2023/10/20 20:34, Matthew Wilcox wrote: >>> On Fri, Oct 20, 2023 at 10:26:31AM +0200, Petr Mladek wrote: >>>> Adding Matthew into Cc in the hope that he is still familiar with the >>>> code. Also adding Andrew who accepts patches. >>> >>> oh joy. i love dealing with cves. >>> >>>>>> I agree, this issue looks to be in kernel-core radix tree code in ./lib/radix-tree.c in two of any places. >>> >>> the radix tree code is the victim here. maybe also the perpetrator, but >>> it's rather hard to say. >>> >>> shrink_slab_memcg() >>> down_read_trylock(&shrinker_rwsem) >>> shrinker = idr_find(&shrinker_idr, i); >>> >>> i assume is the path to this bug. the reporter didn't run the >>> stacktrace through scripts/decode_stacktrace.sh so it's less useful than >>> we might want. >>> >>> prealloc_memcg_shrinker() calls idr_alloc and idr_remove under >>> shrinker_rwsem in write mode, so that should be fine. >>> >>> unregister_memcg_shrinker() calls idr_remove after asserting &shrinker_rwsem >>> is held (although not asserting that it's held for write ... hmm ... but >>> both callers appear to hold it for write anyway) >>> >>> so i don't see why we'd get a UAF here. >>> >>> anyway, adding Qi Zheng to the cc since they're responsible for the >>> shrinker code. >> >> Thanks for CC'ing me, I'd be happy to troubleshoot any issues that may >> be shrinker related. >> >> Between v6.4-rc1 and v6.4 versions, we briefly implemented lockless slab >> shrink using the SRCU method. In these versions, we call idr_alloc and >> idr_remove under shrinker_mutex, and idr_find under srcu_read_lock. >> >> These are all legitimate uses of the IDR APIs and the shrinker_idr >> will never be destroyed, so at a quick glance I didn't see why it would >> cause UAF here. > > I'm not an expert on how all the RCU flavours interact, but I don't > think that's safe. The IDR (radix tree) will RCU-free nodes, but I > don't think holding the srcu_read_lock is enough to prevent the nodes > being freed. Oh, Indeed, I just saw the Documeentation/RCU/checklist.rst: ``` If the updater uses call_rcu() or synchronize_rcu(), then the corresponding readers may use: (1) rcu_read_lock() and rcu_read_unlock(), (2) any pair of primitives that disables and re-enables softirq, for example, rcu_read_lock_bh() and rcu_read_unlock_bh(), or (3) any pair of primitives that disables and re-enables preemption, for example, rcu_read_lock_sched() and rcu_read_unlock_sched(). If the updater uses synchronize_srcu() or call_srcu(), then the corresponding readers must use srcu_read_lock() and srcu_read_unlock(), and with the same srcu_struct. ``` > I think you'd need to take the rcu_read_lock() around > the call to idr_find(). For latest RCU+refcount method, we call idr_find() under rcu_read_lock(), so it's safe. Thanks, Qi > >> Anyway I will keep working on this issue, and it would be nice if >> there was a way to reproduce it. > > So I think the CVE is inappropriately issued. The SRCU code was added in > v6.4-rc1 and removed before v6.4. I don't think CVEs are appropriate for > bugs which only existed in development kernels. How do we revoke CVEs?