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 85734C48BE3 for ; Thu, 20 Jun 2019 18:31:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6526320675 for ; Thu, 20 Jun 2019 18:31:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561055479; bh=LTBT4meJ/uk4ny0lcGwS24hw7IhpJQw+FC/0HzWSDh4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=1/TWTJ/PgUKVWj+NnrykyEvODep5ZsfJNuXESn01WfwQgmlNX0MWt0CcG26B5BYtA P2PGC1HvUjFjuLRVWzkZjRjU8CT/XAdYG//AqVTuJjc2JJbVMG9IRH8TAMQ3Ro5jyd 3/2xKSAGcXX64Yh7Ueukjq7piDD9GxjZdlahf0ko= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726774AbfFTR77 (ORCPT ); Thu, 20 Jun 2019 13:59:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:48182 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726735AbfFTR76 (ORCPT ); Thu, 20 Jun 2019 13:59:58 -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 BD2CA2083B; Thu, 20 Jun 2019 17:59:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561053597; bh=LTBT4meJ/uk4ny0lcGwS24hw7IhpJQw+FC/0HzWSDh4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xs9KE9A3pdorv+31p01n2KEo3bwU6wHhn6SUsSV8usunevx0aVaxdPB8dBD4qb3Ez 5N1NnU6k7IQ8C3M4iYPi4F2H/gNYD2kvzIAKm9YuX3UnjVARJxIeTN3TxcMauIORbT Phb62rvE1RTbrmtmYBblVwZ50V55dY8hPld6pDX0= 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 4.4 45/84] ptrace: restore smp_rmb() in __ptrace_may_access() Date: Thu, 20 Jun 2019 19:56:42 +0200 Message-Id: <20190620174345.297401138@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190620174337.538228162@linuxfoundation.org> References: <20190620174337.538228162@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 @@ -447,6 +447,15 @@ 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 @@ -292,6 +292,16 @@ 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) &&