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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 C584CC3E8AB for ; Sat, 5 Oct 2019 11:28:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 98AFF222C5 for ; Sat, 5 Oct 2019 11:28:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727983AbfJEL2N (ORCPT ); Sat, 5 Oct 2019 07:28:13 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:40128 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726198AbfJEL2N (ORCPT ); Sat, 5 Oct 2019 07:28:13 -0400 Received: from [213.220.153.21] (helo=localhost.localdomain) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1iGiEL-0007UH-Tx; Sat, 05 Oct 2019 11:28:10 +0000 From: Christian Brauner To: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com Cc: bsingharora@gmail.com, elver@google.com, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Christian Brauner Subject: [PATCH] taskstats: fix data-race Date: Sat, 5 Oct 2019 13:28:06 +0200 Message-Id: <20191005112806.13960-1-christian.brauner@ubuntu.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <0000000000009b403005942237bf@google.com> References: <0000000000009b403005942237bf@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When assiging and testing taskstats in taskstats taskstats_exit() there's a race around writing and reading sig->stats. cpu0: task calls exit() do_exit() -> taskstats_exit() -> taskstats_tgid_alloc() The task takes sighand lock and assigns new stats to sig->stats. cpu1: task catches signal do_exit() -> taskstats_tgid_alloc() -> taskstats_exit() The tasks reads sig->stats __without__ holding sighand lock seeing garbage. Fix this by taking sighand lock when reading sig->stats. Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com Signed-off-by: Christian Brauner --- kernel/taskstats.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/kernel/taskstats.c b/kernel/taskstats.c index 13a0f2e6ebc2..58b145234c4a 100644 --- a/kernel/taskstats.c +++ b/kernel/taskstats.c @@ -553,26 +553,32 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info) static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk) { + int empty; + struct taskstats *stats_new, *stats = NULL; struct signal_struct *sig = tsk->signal; - struct taskstats *stats; - - if (sig->stats || thread_group_empty(tsk)) - goto ret; /* No problem if kmem_cache_zalloc() fails */ - stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL); + stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL); + + empty = thread_group_empty(tsk); spin_lock_irq(&tsk->sighand->siglock); + if (sig->stats || empty) { + stats = sig->stats; + spin_unlock_irq(&tsk->sighand->siglock); + goto free_cache; + } + if (!sig->stats) { - sig->stats = stats; - stats = NULL; + sig->stats = stats_new; + spin_unlock_irq(&tsk->sighand->siglock); + return stats_new; } spin_unlock_irq(&tsk->sighand->siglock); - if (stats) - kmem_cache_free(taskstats_cache, stats); -ret: - return sig->stats; +free_cache: + kmem_cache_free(taskstats_cache, stats_new); + return stats; } /* Send pid data out on exit */ -- 2.23.0