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 8FEB7EB64D9 for ; Sun, 2 Jul 2023 19:40:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231296AbjGBTk3 (ORCPT ); Sun, 2 Jul 2023 15:40:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52874 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231320AbjGBTkO (ORCPT ); Sun, 2 Jul 2023 15:40:14 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F29B510D9; Sun, 2 Jul 2023 12:39:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C319660CEB; Sun, 2 Jul 2023 19:39:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2E171C433C9; Sun, 2 Jul 2023 19:39:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1688326756; bh=fSRXvkSoEHCRc62ZWrDhTobb7JgjvIJpvM5rZzK2XuI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n7cF5KjOk1kR1/FZjpaqwCIES5ORwsOK6Lm55brhfPBjgf3UkD4di3+TBlcpp0uqY UKFlOZMi4XK3CIXo0KTWMb2Xa4FQ21We3QfaqCIYcvEZXAATNDyrxPrs97bzoAxkGO ERO3vi5cps6meLjNm82WBdogWA6LbXNpZjP5zSNjk5c4bim5Ph7pEVC1UaE/6R7Ggx UcyFayR6i53O54zA3/9gUWvywZ9j9njqiGE/3kg1rQ1yh92NEkf2thP05K3H61hsiO AtzeYJjSBDO9HV/OUeYUL2XQuMujNw8sObhZwZ6j/Xoo9/Ogg/1WwJG0xzHo3dPzGa sz0aZtqaVYbPA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Zqiang , Joel Fernandes , "Paul E . McKenney" , Sasha Levin , frederic@kernel.org, quic_neeraju@quicinc.com, josh@joshtriplett.org, boqun.feng@gmail.com, rcu@vger.kernel.org Subject: [PATCH AUTOSEL 5.15 2/2] rcu: Protect rcu_print_task_exp_stall() ->exp_tasks access Date: Sun, 2 Jul 2023 15:39:11 -0400 Message-Id: <20230702193911.1776189-2-sashal@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230702193911.1776189-1-sashal@kernel.org> References: <20230702193911.1776189-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.119 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Zqiang [ Upstream commit 3c1566bca3f8349f12b75d0a2d5e4a20ad6262ec ] For kernels built with CONFIG_PREEMPT_RCU=y, the following scenario can result in a NULL-pointer dereference: CPU1 CPU2 rcu_preempt_deferred_qs_irqrestore rcu_print_task_exp_stall if (special.b.blocked) READ_ONCE(rnp->exp_tasks) != NULL raw_spin_lock_rcu_node np = rcu_next_node_entry(t, rnp) if (&t->rcu_node_entry == rnp->exp_tasks) WRITE_ONCE(rnp->exp_tasks, np) .... raw_spin_unlock_irqrestore_rcu_node raw_spin_lock_irqsave_rcu_node t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry) (if rnp->exp_tasks is NULL, this will dereference a NULL pointer) The problem is that CPU2 accesses the rcu_node structure's->exp_tasks field without holding the rcu_node structure's ->lock and CPU2 did not observe CPU1's change to rcu_node structure's ->exp_tasks in time. Therefore, if CPU1 sets rcu_node structure's->exp_tasks pointer to NULL, then CPU2 might dereference that NULL pointer. This commit therefore holds the rcu_node structure's ->lock while accessing that structure's->exp_tasks field. [ paulmck: Apply Frederic Weisbecker feedback. ] Acked-by: Joel Fernandes (Google) Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) Signed-off-by: Sasha Levin --- kernel/rcu/tree_exp.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index f9fb2793b0193..f46c0c1a5eb35 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -708,9 +708,11 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) int ndetected = 0; struct task_struct *t; - if (!READ_ONCE(rnp->exp_tasks)) - return 0; raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!rnp->exp_tasks) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return 0; + } t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { -- 2.39.2