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=-5.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9584FC31E5D for ; Mon, 17 Jun 2019 21:19:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 695452133F for ; Mon, 17 Jun 2019 21:19:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560806366; bh=t1pnHkiMF9SWwsIGha+06k/Ipy6GL626EqbrM5cEYcU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=D1NCydFx3WPnY/gAeuqcLCjgYqGZ3N8fvGTeJvBOk3iG5AFIllm/dSIXEP/6T5dcq iCGhedYSgO8og+uWAmy8IuROGcLcr57O9hawEAOnHa4jWq+Vzo0MkBpRrOwivAgwyU bQe4G2zqqo0PKZp8LYYYusoLRuoPYIQXlUJnj8zM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728803AbfFQVTZ (ORCPT ); Mon, 17 Jun 2019 17:19:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:43160 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728753AbfFQVTX (ORCPT ); Mon, 17 Jun 2019 17:19:23 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8073120861; Mon, 17 Jun 2019 21:19:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1560806363; bh=t1pnHkiMF9SWwsIGha+06k/Ipy6GL626EqbrM5cEYcU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wE1hkPYNgL0wnDFqj2Zuu7qs4UKthEQGLF+79VdtfkqHkeiqDjKVCl6AzhoHBtIZV jGGlrFoHnM1Hj6hEpHZnIjad9JoGec++/JZdZYbXEVMFeyf/RGuH8sotZYfrPdQkWc 4yM11MREmxeX7wBPqUToLSIZ8U5zm+rGjczywtds= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kees Cook , Oleg Nesterov , Jann Horn , "Eric W. Biederman" Subject: [PATCH 5.1 026/115] ptrace: restore smp_rmb() in __ptrace_may_access() Date: Mon, 17 Jun 2019 23:08:46 +0200 Message-Id: <20190617210801.285626070@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190617210759.929316339@linuxfoundation.org> References: <20190617210759.929316339@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jann Horn commit f6581f5b55141a95657ef5742cf6a6bfa20a109f upstream. Restore the read memory barrier in __ptrace_may_access() that was deleted a couple years ago. Also add comments on this barrier and the one it pairs with to explain why they're there (as far as I understand). Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks") Cc: stable@vger.kernel.org Acked-by: Kees Cook Acked-by: Oleg Nesterov Signed-off-by: Jann Horn Signed-off-by: Eric W. Biederman Signed-off-by: Greg Kroah-Hartman --- kernel/cred.c | 9 +++++++++ kernel/ptrace.c | 10 ++++++++++ 2 files changed, 19 insertions(+) --- a/kernel/cred.c +++ b/kernel/cred.c @@ -450,6 +450,15 @@ int commit_creds(struct cred *new) if (task->mm) set_dumpable(task->mm, suid_dumpable); task->pdeath_signal = 0; + /* + * If a task drops privileges and becomes nondumpable, + * the dumpability change must become visible before + * the credential change; otherwise, a __ptrace_may_access() + * racing with this change may be able to attach to a task it + * shouldn't be able to attach to (as if the task had dropped + * privileges without becoming nondumpable). + * Pairs with a read barrier in __ptrace_may_access(). + */ smp_wmb(); } --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -323,6 +323,16 @@ static int __ptrace_may_access(struct ta return -EPERM; ok: rcu_read_unlock(); + /* + * If a task drops privileges and becomes nondumpable (through a syscall + * like setresuid()) while we are trying to access it, we must ensure + * that the dumpability is read after the credentials; otherwise, + * we may be able to attach to a task that we shouldn't be able to + * attach to (as if the task had dropped privileges without becoming + * nondumpable). + * Pairs with a write barrier in commit_creds(). + */ + smp_rmb(); mm = task->mm; if (mm && ((get_dumpable(mm) != SUID_DUMP_USER) &&