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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9E15EC4363A for ; Mon, 12 Oct 2020 19:03:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 52C3821D81 for ; Mon, 12 Oct 2020 19:03:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602529390; bh=Kmkb6hRz4+TOx950kSgcQvZxH2dY+imBL1JTQWpMf0U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=abdqXdQjJ4rvSDEOCEVxfR4t1yta1z7BToFQh4wn5K96t0mFo2juoLlCm48RwAK1G xcNRRwbAdP1SUdVlNy1i2ZgAnoXUJqhtSXTwLMMLDchhuijwfybF8tsHFj1SmAnVDK hhNzqWpkahxKqF3bUa6YMsjxf3JppO7sZ9QJc87k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390131AbgJLTDI (ORCPT ); Mon, 12 Oct 2020 15:03:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:52452 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389663AbgJLTDF (ORCPT ); Mon, 12 Oct 2020 15:03:05 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B65CE2067C; Mon, 12 Oct 2020 19:03:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602529384; bh=Kmkb6hRz4+TOx950kSgcQvZxH2dY+imBL1JTQWpMf0U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cN0Uet3OrcpMUSngD93Gtf4JFcQi6O0V2BY6+3G1bZTykpg6+ioj6I3XSeKDqF76C J1T8ivBI1RFwD1U1+++LXR6WIKOMF4XERkBuPyhG+xKulD7u2NpiYqKwU1eaqCtKNA yiknElqhGODxzdePxmCdaVPxEsu+M17cxgp9RjdM= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Linus Torvalds , Vegard Nossum , Al Viro , "Eric W . Biederman" , Sasha Levin Subject: [PATCH AUTOSEL 5.8 19/24] usermodehelper: reset umask to default before executing user process Date: Mon, 12 Oct 2020 15:02:34 -0400 Message-Id: <20201012190239.3279198-19-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201012190239.3279198-1-sashal@kernel.org> References: <20201012190239.3279198-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds [ Upstream commit 4013c1496c49615d90d36b9d513eee8e369778e9 ] Kernel threads intentionally do CLONE_FS in order to follow any changes that 'init' does to set up the root directory (or cwd). It is admittedly a bit odd, but it avoids the situation where 'init' does some extensive setup to initialize the system environment, and then we execute a usermode helper program, and it uses the original FS setup from boot time that may be very limited and incomplete. [ Both Al Viro and Eric Biederman point out that 'pivot_root()' will follow the root regardless, since it fixes up other users of root (see chroot_fs_refs() for details), but overmounting root and doing a chroot() would not. ] However, Vegard Nossum noticed that the CLONE_FS not only means that we follow the root and current working directories, it also means we share umask with whatever init changed it to. That wasn't intentional. Just reset umask to the original default (0022) before actually starting the usermode helper program. Reported-by: Vegard Nossum Cc: Al Viro Acked-by: Eric W. Biederman Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/umh.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/umh.c b/kernel/umh.c index 79f139a7ca03c..6aaf456d402d9 100644 --- a/kernel/umh.c +++ b/kernel/umh.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include #include @@ -75,6 +76,14 @@ static int call_usermodehelper_exec_async(void *data) flush_signal_handlers(current, 1); spin_unlock_irq(¤t->sighand->siglock); + /* + * Initial kernel threads share ther FS with init, in order to + * get the init root directory. But we've now created a new + * thread that is going to execve a user process and has its own + * 'struct fs_struct'. Reset umask to the default. + */ + current->fs->umask = 0022; + /* * Our parent (unbound workqueue) runs with elevated scheduling * priority. Avoid propagating that into the userspace child. -- 2.25.1