From patchwork Mon Jun 20 12:51:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 12887569 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BA7ACCA482 for ; Mon, 20 Jun 2022 13:06:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244935AbiFTNGD (ORCPT ); Mon, 20 Jun 2022 09:06:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244450AbiFTNFW (ORCPT ); Mon, 20 Jun 2022 09:05:22 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9ABB519C24; Mon, 20 Jun 2022 06:00:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 10DD4B811A6; Mon, 20 Jun 2022 13:00:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29CE9C3411B; Mon, 20 Jun 2022 13:00:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1655730011; bh=WaG1nHyRp9gM42Yl11WvQkmWsXZ9kxeW+GdjIh4gZQ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=neck4NhXlgyFTZVyO1V8lKwrP4EVn6Zu3igtZNX+fkO38djIZIRYvK42qYL8yGZmV 02leBcLKj0NW6UAVyLQSNm+mAFDx3Lke8+kDGHhprnFminAPl16XUL53JU0MphfHC1 ynrG+MU9PtXMthTV7JfMwHtusnhmojboK4IQ1gqY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Seth Forshee , Christoph Hellwig , Aleksa Sarai , Al Viro , linux-fsdevel@vger.kernel.org, "Christian Brauner (Microsoft)" Subject: [PATCH 5.18 125/141] fs: account for group membership Date: Mon, 20 Jun 2022 14:51:03 +0200 Message-Id: <20220620124733.247984907@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220620124729.509745706@linuxfoundation.org> References: <20220620124729.509745706@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Christian Brauner commit 168f912893407a5acb798a4a58613b5f1f98c717 upstream. When calling setattr_prepare() to determine the validity of the attributes the ia_{g,u}id fields contain the value that will be written to inode->i_{g,u}id. This is exactly the same for idmapped and non-idmapped mounts and allows callers to pass in the values they want to see written to inode->i_{g,u}id. When group ownership is changed a caller whose fsuid owns the inode can change the group of the inode to any group they are a member of. When searching through the caller's groups we need to use the gid mapped according to the idmapped mount otherwise we will fail to change ownership for unprivileged users. Consider a caller running with fsuid and fsgid 1000 using an idmapped mount that maps id 65534 to 1000 and 65535 to 1001. Consequently, a file owned by 65534:65535 in the filesystem will be owned by 1000:1001 in the idmapped mount. The caller now requests the gid of the file to be changed to 1000 going through the idmapped mount. In the vfs we will immediately map the requested gid to the value that will need to be written to inode->i_gid and place it in attr->ia_gid. Since this idmapped mount maps 65534 to 1000 we place 65534 in attr->ia_gid. When we check whether the caller is allowed to change group ownership we first validate that their fsuid matches the inode's uid. The inode->i_uid is 65534 which is mapped to uid 1000 in the idmapped mount. Since the caller's fsuid is 1000 we pass the check. We now check whether the caller is allowed to change inode->i_gid to the requested gid by calling in_group_p(). This will compare the passed in gid to the caller's fsgid and search the caller's additional groups. Since we're dealing with an idmapped mount we need to pass in the gid mapped according to the idmapped mount. This is akin to checking whether a caller is privileged over the future group the inode is owned by. And that needs to take the idmapped mount into account. Note, all helpers are nops without idmapped mounts. New regression test sent to xfstests. Link: https://github.com/lxc/lxd/issues/10537 Link: https://lore.kernel.org/r/20220613111517.2186646-1-brauner@kernel.org Fixes: 2f221d6f7b88 ("attr: handle idmapped mounts") Cc: Seth Forshee Cc: Christoph Hellwig Cc: Aleksa Sarai Cc: Al Viro Cc: stable@vger.kernel.org # 5.15+ CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee Signed-off-by: Christian Brauner (Microsoft) Signed-off-by: Greg Kroah-Hartman --- fs/attr.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) --- a/fs/attr.c +++ b/fs/attr.c @@ -61,9 +61,15 @@ static bool chgrp_ok(struct user_namespa const struct inode *inode, kgid_t gid) { kgid_t kgid = i_gid_into_mnt(mnt_userns, inode); - if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) && - (in_group_p(gid) || gid_eq(gid, inode->i_gid))) - return true; + if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) { + kgid_t mapped_gid; + + if (gid_eq(gid, inode->i_gid)) + return true; + mapped_gid = mapped_kgid_fs(mnt_userns, i_user_ns(inode), gid); + if (in_group_p(mapped_gid)) + return true; + } if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_CHOWN)) return true; if (gid_eq(kgid, INVALID_GID) && @@ -123,12 +129,20 @@ int setattr_prepare(struct user_namespac /* Make sure a caller can chmod. */ if (ia_valid & ATTR_MODE) { + kgid_t mapped_gid; + if (!inode_owner_or_capable(mnt_userns, inode)) return -EPERM; + + if (ia_valid & ATTR_GID) + mapped_gid = mapped_kgid_fs(mnt_userns, + i_user_ns(inode), attr->ia_gid); + else + mapped_gid = i_gid_into_mnt(mnt_userns, inode); + /* Also check the setgid bit! */ - if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid : - i_gid_into_mnt(mnt_userns, inode)) && - !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) + if (!in_group_p(mapped_gid) && + !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID)) attr->ia_mode &= ~S_ISGID; }