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 5187CC43334 for ; Fri, 3 Jun 2022 18:30:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347046AbiFCSay (ORCPT ); Fri, 3 Jun 2022 14:30:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347804AbiFCSaC (ORCPT ); Fri, 3 Jun 2022 14:30:02 -0400 Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73F8A72220 for ; Fri, 3 Jun 2022 11:13:42 -0700 (PDT) Received: by mail-pf1-x431.google.com with SMTP id j6so7698228pfe.13 for ; Fri, 03 Jun 2022 11:13:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=KMzrP1ZYW7q/TidHk4y7Aa/yx0iJcaya5gROyIWR4BM=; b=SIwXH7tnxO54DrmpfWx37Dnzpuo94VKI4hgsLJaP4UwHqx2y2++HlfNfMVE+I2W/OA DUcWVfaaS3FYE/N/cVWCzSVDG8dVCzDAgWFJIbqQ1j0VPI0piNoE9hSLj778PbA3UH6C 6gtRw0QFXRiEqGe1/XrP/ujAJQzyzpXfBnKUpojGztmXaIiEngCdDgiBWLk1xXxzdr0M MMJ9NQpVcTv2f2MR5gCqrUzYHtZFH+Vrg6QFG9WvpHcbvevt8i8fho6MC5p+/6paQMc9 68coNPXUYF9IIDxSI8QlwNpmBrzAhtXGPCCfPUMjDEoKMo5g16cE/n016vt6Pe0PiiJu +nrQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=KMzrP1ZYW7q/TidHk4y7Aa/yx0iJcaya5gROyIWR4BM=; b=Z7kooouR+zLSNlAXJ/wKEc3WhN17MQe8ZYcWJ4p3g5L85GMpRv0MRQmpXbrLxqA7aP JmHSVLLL3alAZEwetLi/cUJwGtEFeZBZZ4QQy9FvlbiGQ4X/nVGjXQG0xxtSl4BXMBtK /9yx0l0Dv1yFPHQwY+GBl9avGxrlXv3/1DOOAimGTwaAfSAKs4i0SkLtCb3xVsDWrZa6 vzRly1oL12sCvCq/VR45C9zHKsd5SKbNve0SWYsBT0FUw4Rc6lXAYNidZQzPZsIJFlhH 0LxoauaPNQVRBeTziowHXPSG+yWdq8qb9I0e0MzeyZ+yOCZRAOwW1vcIPaIIpeFSq2+a gyWg== X-Gm-Message-State: AOAM531dCaLuHiS8dUDXguzSDcG7w7CblSyg8U1t8bv/fjEfszfVwGdv Uy7tqmLi0JjAiX1sNPvgF9n4OQ== X-Google-Smtp-Source: ABdhPJx6Fhx/k/G6F3rQ2T+mGOIPbpXrjtVEn/vidFgj5AVDqH7jNxEZNkDQfzwCOOGN+vAN2KhRAQ== X-Received: by 2002:a05:6a00:2396:b0:51b:de97:7efe with SMTP id f22-20020a056a00239600b0051bde977efemr5437281pfc.8.1654280014264; Fri, 03 Jun 2022 11:13:34 -0700 (PDT) Received: from localhost.localdomain ([50.39.160.154]) by smtp.gmail.com with ESMTPSA id e8-20020a170902784800b001640ab19773sm5853198pln.58.2022.06.03.11.13.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Jun 2022 11:13:33 -0700 (PDT) From: Tadeusz Struk To: Tejun Heo Cc: Tadeusz Struk , Michal Koutny , Zefan Li , Johannes Weiner , Christian Brauner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , cgroups@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, stable@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+e42ae441c3b10acf9e9d@syzkaller.appspotmail.com Subject: [PATCH v2] cgroup: serialize css kill and release paths Date: Fri, 3 Jun 2022 11:13:21 -0700 Message-Id: <20220603181321.443716-1-tadeusz.struk@linaro.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220603173455.441537-1-tadeusz.struk@linaro.org> References: <20220603173455.441537-1-tadeusz.struk@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Syzbot found a corrupted list bug scenario that can be triggered from cgroup_subtree_control_write(cgrp). The reproduces writes to cgroup.subtree_control file, which invokes: cgroup_apply_control_enable()->css_create()->css_populate_dir(), which then fails with a fault injected -ENOMEM. In such scenario the css_killed_work_fn will be en-queued via cgroup_apply_control_disable(cgrp)->kill_css(css), and bail out to cgroup_kn_unlock(). Then cgroup_kn_unlock() will call: cgroup_put(cgrp)->css_put(&cgrp->self), which will try to enqueue css_release_work_fn for the same css instance, causing a list_add corruption bug, as can be seen in the syzkaller report [1]. Fix this by synchronizing the css ref_kill and css_release jobs. css_release() function will check if the css_killed_work_fn() has been scheduled for the css and only en-queue the css_release_work_fn() if css_killed_work_fn wasn't already en-queued. Otherwise css_release() will set the CSS_REL_LATER flag for that css. This will cause the css_release_work_fn() work to be executed after css_killed_work_fn() is finished. Two scc flags have been introduced to implement this serialization mechanizm: * CSS_KILL_ENQED, which will be set when css_killed_work_fn() is en-queued, and * CSS_REL_LATER, which, if set, will cause the css_release_work_fn() to be scheduled after the css_killed_work_fn is finished. There is also a new lock, which will protect the integrity of the css flags. [1] https://syzkaller.appspot.com/bug?id=e26e54d6eac9d9fb50b221ec3e4627b327465dbd Cc: Tejun Heo Cc: Michal Koutny Cc: Zefan Li Cc: Johannes Weiner Cc: Christian Brauner Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: Andrii Nakryiko Cc: Martin KaFai Lau Cc: Song Liu Cc: Yonghong Song Cc: John Fastabend Cc: KP Singh Cc: Cc: Cc: Cc: Cc: Reported-and-tested-by: syzbot+e42ae441c3b10acf9e9d@syzkaller.appspotmail.com Fixes: 8f36aaec9c92 ("cgroup: Use rcu_work instead of explicit rcu and work item") Signed-off-by: Tadeusz Struk --- v2: Use correct lock in css_killed_work_fn() --- include/linux/cgroup-defs.h | 4 ++++ kernel/cgroup/cgroup.c | 35 ++++++++++++++++++++++++++++++++--- 2 files changed, 36 insertions(+), 3 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 1bfcfb1af352..8dc8b4edb242 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -53,6 +53,8 @@ enum { CSS_RELEASED = (1 << 2), /* refcnt reached zero, released */ CSS_VISIBLE = (1 << 3), /* css is visible to userland */ CSS_DYING = (1 << 4), /* css is dying */ + CSS_KILL_ENQED = (1 << 5), /* kill work enqueued for the css */ + CSS_REL_LATER = (1 << 6), /* release needs to be done after kill */ }; /* bits in struct cgroup flags field */ @@ -162,6 +164,8 @@ struct cgroup_subsys_state { */ int id; + /* lock to protect flags */ + spinlock_t lock; unsigned int flags; /* diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 1779ccddb734..b1bbd438d426 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5210,8 +5210,23 @@ static void css_release(struct percpu_ref *ref) struct cgroup_subsys_state *css = container_of(ref, struct cgroup_subsys_state, refcnt); - INIT_WORK(&css->destroy_work, css_release_work_fn); - queue_work(cgroup_destroy_wq, &css->destroy_work); + spin_lock_bh(&css->lock); + + /* + * Check if the css_killed_work_fn work has been scheduled for this + * css and enqueue css_release_work_fn only if it wasn't. + * Otherwise set the CSS_REL_LATER flag, which will cause + * release to be enqueued after css_killed_work_fn is finished. + * This is to prevent list corruption by en-queuing two instance + * of the same work struct on the same WQ, namely cgroup_destroy_wq. + */ + if (!(css->flags & CSS_KILL_ENQED)) { + INIT_WORK(&css->destroy_work, css_release_work_fn); + queue_work(cgroup_destroy_wq, &css->destroy_work); + } else { + css->flags |= CSS_REL_LATER; + } + spin_unlock_bh(&css->lock); } static void init_and_link_css(struct cgroup_subsys_state *css, @@ -5230,6 +5245,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css, INIT_LIST_HEAD(&css->rstat_css_node); css->serial_nr = css_serial_nr_next++; atomic_set(&css->online_cnt, 0); + spin_lock_init(&css->lock); if (cgroup_parent(cgrp)) { css->parent = cgroup_css(cgroup_parent(cgrp), ss); @@ -5545,10 +5561,12 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode) */ static void css_killed_work_fn(struct work_struct *work) { - struct cgroup_subsys_state *css = + struct cgroup_subsys_state *css_killed, *css = container_of(work, struct cgroup_subsys_state, destroy_work); mutex_lock(&cgroup_mutex); + css_killed = css; + css_killed->flags &= ~CSS_KILL_ENQED; do { offline_css(css); @@ -5557,6 +5575,14 @@ static void css_killed_work_fn(struct work_struct *work) css = css->parent; } while (css && atomic_dec_and_test(&css->online_cnt)); + spin_lock_bh(&css_killed->lock); + if (css_killed->flags & CSS_REL_LATER) { + /* If css_release work was delayed for the css enqueue it now. */ + INIT_WORK(&css_killed->destroy_work, css_release_work_fn); + queue_work(cgroup_destroy_wq, &css_killed->destroy_work); + css_killed->flags &= ~CSS_REL_LATER; + } + spin_unlock_bh(&css_killed->lock); mutex_unlock(&cgroup_mutex); } @@ -5566,10 +5592,13 @@ static void css_killed_ref_fn(struct percpu_ref *ref) struct cgroup_subsys_state *css = container_of(ref, struct cgroup_subsys_state, refcnt); + spin_lock_bh(&css->lock); if (atomic_dec_and_test(&css->online_cnt)) { + css->flags |= CSS_KILL_ENQED; INIT_WORK(&css->destroy_work, css_killed_work_fn); queue_work(cgroup_destroy_wq, &css->destroy_work); } + spin_unlock_bh(&css->lock); } /** -- 2.36.1