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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 746A5C433EF for ; Thu, 30 Jun 2022 14:10:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236737AbiF3OKo (ORCPT ); Thu, 30 Jun 2022 10:10:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236427AbiF3OKP (ORCPT ); Thu, 30 Jun 2022 10:10:15 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 43D1A7B34D; Thu, 30 Jun 2022 06:55:32 -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 EC59CB82AF8; Thu, 30 Jun 2022 13:55:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 661FAC34115; Thu, 30 Jun 2022 13:55:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656597325; bh=n6pCRpxRo1ejolie+HwU9V9duHfbqPeFU7Zrwi/AZt0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lXG8VpV5r34mtYYBUDk6FuRXKXKOZiFgU+0Hh8mtsIUKDKgZgVj77H/dvaPckOYsp GypL8nqyj97UJiOaQREneOYzXSrPCuDl0BTS7vdKozTlxGun7a0xym8sNqVhLy7LsJ gN7QDH0Uj13znq4+ZIxmeh+iOY2+mquXH12Wj0cI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Seth Forshee , Amir Goldstein , Christoph Hellwig , Al Viro , linux-fsdevel@vger.kernel.org, Christian Brauner , "Christian Brauner (Microsoft)" Subject: [PATCH 5.15 17/28] docs: update mapping documentation Date: Thu, 30 Jun 2022 15:47:13 +0200 Message-Id: <20220630133233.434921899@linuxfoundation.org> X-Mailer: git-send-email 2.37.0 In-Reply-To: <20220630133232.926711493@linuxfoundation.org> References: <20220630133232.926711493@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Christian Brauner commit 8cc5c54de44c5e8e104d364a627ac4296845fc7f upstream. Now that we implement the full remapping algorithms described in our documentation remove the section about shortcircuting them. Link: https://lore.kernel.org/r/20211123114227.3124056-6-brauner@kernel.org (v1) Link: https://lore.kernel.org/r/20211130121032.3753852-6-brauner@kernel.org (v2) Link: https://lore.kernel.org/r/20211203111707.3901969-6-brauner@kernel.org Cc: Seth Forshee Cc: Amir Goldstein Cc: Christoph Hellwig Cc: Al Viro CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee Signed-off-by: Christian Brauner Signed-off-by: Christian Brauner (Microsoft) Signed-off-by: Greg Kroah-Hartman --- Documentation/filesystems/idmappings.rst | 72 ------------------------------- 1 file changed, 72 deletions(-) --- a/Documentation/filesystems/idmappings.rst +++ b/Documentation/filesystems/idmappings.rst @@ -952,75 +952,3 @@ The raw userspace id that is put on disk their home directory back to their home computer where they are assigned ``u1000`` using the initial idmapping and mount the filesystem with the initial idmapping they will see all those files owned by ``u1000``. - -Shortcircuting --------------- - -Currently, the implementation of idmapped mounts enforces that the filesystem -is mounted with the initial idmapping. The reason is simply that none of the -filesystems that we targeted were mountable with a non-initial idmapping. But -that might change soon enough. As we've seen above, thanks to the properties of -idmappings the translation works for both filesystems mounted with the initial -idmapping and filesystem with non-initial idmappings. - -Based on this current restriction to filesystem mounted with the initial -idmapping two noticeable shortcuts have been taken: - -1. We always stash a reference to the initial user namespace in ``struct - vfsmount``. Idmapped mounts are thus mounts that have a non-initial user - namespace attached to them. - - In order to support idmapped mounts this needs to be changed. Instead of - stashing the initial user namespace the user namespace the filesystem was - mounted with must be stashed. An idmapped mount is then any mount that has - a different user namespace attached then the filesystem was mounted with. - This has no user-visible consequences. - -2. The translation algorithms in ``mapped_fs*id()`` and ``i_*id_into_mnt()`` - are simplified. - - Let's consider ``mapped_fs*id()`` first. This function translates the - caller's kernel id into a kernel id in the filesystem's idmapping via - a mount's idmapping. The full algorithm is:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - make_kuid(filesystem-idmapping, uid) = kuid - - We know that the filesystem is always mounted with the initial idmapping as - we enforce this in ``mount_setattr()``. So this can be shortened to:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - KUIDT_INIT(uid) = kuid - - Similarly, for ``i_*id_into_mnt()`` which translated the filesystem's kernel - id into a mount's kernel id:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - from_kuid(filesystem-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - - Again, we know that the filesystem is always mounted with the initial - idmapping as we enforce this in ``mount_setattr()``. So this can be - shortened to:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - __kuid_val(kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - -Handling filesystems mounted with non-initial idmappings requires that the -translation functions be converted to their full form. They can still be -shortcircuited on non-idmapped mounts. This has no user-visible consequences.