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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,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 8F54DC282C3 for ; Thu, 24 Jan 2019 19:29:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 59AC9218F0 for ; Thu, 24 Jan 2019 19:29:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548358161; bh=duGUUSRAk2aDiZgkaCLu9fA0RM7SnJZUVIWAXxJEkV4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sGIFhX4I6f7xjb5idhZJEP0r1A1bHTi4bv4yo0Duug5tcvVXXozjAWCfqlLwM1eTv gevxF45gzjKWQxZZE3B7XY3UDhJ/0ifddHRzEUVj6TGs/6+ZT9X0//bNwCsBt5i+IH N+yzgweGIifUMVXcv4nxBjhgkOtaVuc5GN0XJMRk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730736AbfAXT3U (ORCPT ); Thu, 24 Jan 2019 14:29:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:56206 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731113AbfAXT3K (ORCPT ); Thu, 24 Jan 2019 14:29:10 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.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 0FC90218E2; Thu, 24 Jan 2019 19:29:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548358149; bh=duGUUSRAk2aDiZgkaCLu9fA0RM7SnJZUVIWAXxJEkV4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=j3h3oxDBFILgDyPVvGDXmZfokTXL4u8U5v76YHyLLl+Va65vJX6vv6Ftj3yVbdZ5B ZKSESlTQGkbw8CJy55dMBXou9q1DC0vF9bcssZlSSYuSm94NJAmf83LPDyUUry3BXU YAtw0kHF6XYeB9VhjJgO+1V/HM1ddgQeAvA6E74c= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ondrej Mosnacek , Paul Moore , Sasha Levin Subject: [PATCH 4.9 11/39] selinux: always allow mounting submounts Date: Thu, 24 Jan 2019 20:20:14 +0100 Message-Id: <20190124190448.630960639@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190124190448.232316246@linuxfoundation.org> References: <20190124190448.232316246@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore 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 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 2cbdcb882f97a45f7475c67ac6257bbc16277dfe ] If a superblock has the MS_SUBMOUNT flag set, we should always allow mounting it. These mounts are done automatically by the kernel either as part of mounting some parent mount (e.g. debugfs always mounts tracefs under "tracing" for compatibility) or they are mounted automatically as needed on subdirectory accesses (e.g. NFS crossmnt mounts). Since such automounts are either an implicit consequence of the parent mount (which is already checked) or they can happen during regular accesses (where it doesn't make sense to check against the current task's context), the mount permission check should be skipped for them. Without this patch, attempts to access contents of an automounted directory can cause unexpected SELinux denials. In the current kernel tree, the MS_SUBMOUNT flag is set only via vfs_submount(), which is called only from the following places: - AFS, when automounting special "symlinks" referencing other cells - CIFS, when automounting "referrals" - NFS, when automounting subtrees - debugfs, when automounting tracefs In all cases the submounts are meant to be transparent to the user and it makes sense that if mounting the master is allowed, then so should be the automounts. Note that CAP_SYS_ADMIN capability checking is already skipped for (SB_KERNMOUNT|SB_SUBMOUNT) in: - sget_userns() in fs/super.c: if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !(type->fs_flags & FS_USERNS_MOUNT) && !capable(CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); - sget() in fs/super.c: /* Ensure the requestor has permissions over the target filesystem */ if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); Verified internally on patched RHEL 7.6 with a reproducer using NFS+httpd and selinux-tesuite. Fixes: 93faccbbfa95 ("fs: Better permission checking for submounts") Signed-off-by: Ondrej Mosnacek Signed-off-by: Paul Moore Signed-off-by: Sasha Levin --- security/selinux/hooks.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 8ded80867b92..d293b546a2aa 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2758,7 +2758,7 @@ static int selinux_sb_kern_mount(struct super_block *sb, int flags, void *data) return rc; /* Allow all mounts performed by the kernel */ - if (flags & MS_KERNMOUNT) + if (flags & (MS_KERNMOUNT | MS_SUBMOUNT)) return 0; ad.type = LSM_AUDIT_DATA_DENTRY; -- 2.19.1