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 X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5C46C43461 for ; Wed, 12 May 2021 17:41:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E571613C8 for ; Wed, 12 May 2021 17:41:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348569AbhELRh5 (ORCPT ); Wed, 12 May 2021 13:37:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:36282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239661AbhELQKk (ORCPT ); Wed, 12 May 2021 12:10:40 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 04D6B61C73; Wed, 12 May 2021 15:40:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1620834037; bh=gHliNVVaIsD5pFgsFAKujYOVmUdZfxy9Cj+gveNlQd8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Um9GXlLD7nVS0dLBaxLNb5HUnpEJ42po1wVJUiGT+J1IHk5IKT9Cp6kOuhquj6bN4 9GxpHQ/h7IPMbQWug4Sk4LH5Ak1igNUn8r9fpAl/QApLCxLei8pzl1tYL1kLwk1H57 SrVg0JkaA4ZyUavo7mJ9r8cMnIk8qnwoSa9YUR1U= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Peter Zijlstra (Intel)" , Valentin Schneider , Sasha Levin Subject: [PATCH 5.11 385/601] kthread: Fix PF_KTHREAD vs to_kthread() race Date: Wed, 12 May 2021 16:47:42 +0200 Message-Id: <20210512144840.475138731@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210512144827.811958675@linuxfoundation.org> References: <20210512144827.811958675@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ Upstream commit 3a7956e25e1d7b3c148569e78895e1f3178122a9 ] The kthread_is_per_cpu() construct relies on only being called on PF_KTHREAD tasks (per the WARN in to_kthread). This gives rise to the following usage pattern: if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) However, as reported by syzcaller, this is broken. The scenario is: CPU0 CPU1 (running p) (p->flags & PF_KTHREAD) // true begin_new_exec() me->flags &= ~(PF_KTHREAD|...); kthread_is_per_cpu(p) to_kthread(p) WARN(!(p->flags & PF_KTHREAD) <-- *SPLAT* Introduce __to_kthread() that omits the WARN and is sure to check both values. Use this to remove the problematic pattern for kthread_is_per_cpu() and fix a number of other kthread_*() functions that have similar issues but are currently not used in ways that would expose the problem. Notably kthread_func() is only ever called on 'current', while kthread_probe_data() is only used for PF_WQ_WORKER, which implies the task is from kthread_create*(). Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU") Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Link: https://lkml.kernel.org/r/YH6WJc825C4P0FCK@hirez.programming.kicks-ass.net Signed-off-by: Sasha Levin --- kernel/kthread.c | 33 +++++++++++++++++++++++++++------ kernel/sched/core.c | 2 +- kernel/sched/fair.c | 2 +- 3 files changed, 29 insertions(+), 8 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index 1578973c5740..6d3c488a0f82 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -84,6 +84,25 @@ static inline struct kthread *to_kthread(struct task_struct *k) return (__force void *)k->set_child_tid; } +/* + * Variant of to_kthread() that doesn't assume @p is a kthread. + * + * Per construction; when: + * + * (p->flags & PF_KTHREAD) && p->set_child_tid + * + * the task is both a kthread and struct kthread is persistent. However + * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and + * begin_new_exec()). + */ +static inline struct kthread *__to_kthread(struct task_struct *p) +{ + void *kthread = (__force void *)p->set_child_tid; + if (kthread && !(p->flags & PF_KTHREAD)) + kthread = NULL; + return kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_should_stop); */ void *kthread_func(struct task_struct *task) { - if (task->flags & PF_KTHREAD) - return to_kthread(task)->threadfn; + struct kthread *kthread = __to_kthread(task); + if (kthread) + return kthread->threadfn; return NULL; } EXPORT_SYMBOL_GPL(kthread_func); @@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data); */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); + if (kthread) + copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); return data; } @@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_struct *k, int cpu) set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); } -bool kthread_is_per_cpu(struct task_struct *k) +bool kthread_is_per_cpu(struct task_struct *p) { - struct kthread *kthread = to_kthread(k); + struct kthread *kthread = __to_kthread(p); if (!kthread) return false; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f0056507a373..c5fcb5ce2194 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7290,7 +7290,7 @@ static void balance_push(struct rq *rq) * histerical raisins. */ if (rq->idle == push_task || - ((push_task->flags & PF_KTHREAD) && kthread_is_per_cpu(push_task)) || + kthread_is_per_cpu(push_task) || is_migration_disabled(push_task)) { /* diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d9182af98988..f217e5251fb2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7588,7 +7588,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) return 0; /* Disregard pcpu kthreads; they are where they need to be. */ - if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) + if (kthread_is_per_cpu(p)) return 0; if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) { -- 2.30.2