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=-9.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 5D2E5C43457 for ; Fri, 9 Oct 2020 18:16:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12C6722284 for ; Fri, 9 Oct 2020 18:16:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eWo+rl/D" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389511AbgJISQs (ORCPT ); Fri, 9 Oct 2020 14:16:48 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55350 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731198AbgJISQl (ORCPT ); Fri, 9 Oct 2020 14:16:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602267399; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=f1O55K6rmGWiDD2mmxn/ros/bBH3lRJCLyuGLJc5wtM=; b=eWo+rl/DqRkdc3Kh/Rjzni2A8YfWuItGDVTTVbcz0m+LuMDlrWE+yF/tdKmU7RjvshkmoS xlY0As6cEEfjW/bOEA9/HbvUHFqEAtghqMZKIoO+xJ6na9ol+883PE1XKu8nBxACypX0Np mSz1QzxgLP5ycXYkR8u7HpRyttkyMyg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-39-u30Eb3UBPLGJmYwjUDZ-Xw-1; Fri, 09 Oct 2020 14:16:38 -0400 X-MC-Unique: u30Eb3UBPLGJmYwjUDZ-Xw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0E0AE1008557; Fri, 9 Oct 2020 18:16:37 +0000 (UTC) Received: from horse.redhat.com (ovpn-115-194.rdu2.redhat.com [10.10.115.194]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4D40A10023A7; Fri, 9 Oct 2020 18:16:33 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id D800A223AB2; Fri, 9 Oct 2020 14:16:32 -0400 (EDT) From: Vivek Goyal To: linux-fsdevel@vger.kernel.org, miklos@szeredi.hu Cc: vgoyal@redhat.com, virtio-fs@redhat.com Subject: [PATCH v3 1/6] fuse: Introduce the notion of FUSE_HANDLE_KILLPRIV_V2 Date: Fri, 9 Oct 2020 14:15:07 -0400 Message-Id: <20201009181512.65496-2-vgoyal@redhat.com> In-Reply-To: <20201009181512.65496-1-vgoyal@redhat.com> References: <20201009181512.65496-1-vgoyal@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org We already have FUSE_HANDLE_KILLPRIV flag that says that file server will remove suid/sgid/caps on truncate/chown/write. But that's little different from what Linux VFS implements. To be consistent with Linux VFS behavior what we want is. - caps are always cleared on chown/write/truncate - suid is always cleared on chown, while for truncate/write it is cleared only if caller does not have CAP_FSETID. - sgid is always cleared on chown, while for truncate/write it is cleared only if caller does not have CAP_FSETID as well as file has group execute permission. As previous flag did not provide above semantics. Implement a V2 of the protocol with above said constraints. Server does not know if caller has CAP_FSETID or not. So for the case of write()/truncate(), client will send information in special flag to indicate whether to kill priviliges or not. These changes are in subsequent patches. FUSE_HANDLE_KILLPRIV_V2 relies on WRITE being sent to server to clear suid/sgid/security.capability. But with ->writeback_cache, WRITES are cached in guest. So it is not recommended to use FUSE_HANDLE_KILLPRIV_V2 and writeback_cache together. Though it probably might be good enough for lot of use cases. Signed-off-by: Vivek Goyal --- fs/fuse/fuse_i.h | 6 ++++++ fs/fuse/inode.c | 5 ++++- include/uapi/linux/fuse.h | 7 +++++++ 3 files changed, 17 insertions(+), 1 deletion(-) diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index dbaae2f6c73e..3dd1578be405 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -631,6 +631,12 @@ struct fuse_conn { /* show legacy mount options */ unsigned int legacy_opts_show:1; + /** fs kills suid/sgid/cap on write/chown/trunc. suid is + killed on write/trunc only if caller did not have CAP_FSETID. + sgid is killed on write/truncate only if caller did not have + CAP_FSETID as well as file has group execute permission. */ + unsigned handle_killpriv_v2:1; + /* * The following bitfields are only for optimization purposes * and hence races in setting them will not cause malfunction diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c index d252237219bf..20740b61f12b 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -993,6 +993,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_args *args, !fuse_dax_check_alignment(fc, arg->map_alignment)) { ok = false; } + if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) + fc->handle_killpriv_v2 = 1; } else { ra_pages = fc->max_read / PAGE_SIZE; fc->no_lock = 1; @@ -1035,7 +1037,8 @@ void fuse_send_init(struct fuse_conn *fc) FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT | FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL | FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS | - FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA; + FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA | + FUSE_HANDLE_KILLPRIV_V2; #ifdef CONFIG_FUSE_DAX if (fc->dax) ia->in.flags |= FUSE_MAP_ALIGNMENT; diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 8899e4862309..3ae3f222a0ed 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -172,6 +172,7 @@ * - add FUSE_WRITE_KILL_PRIV flag * - add FUSE_SETUPMAPPING and FUSE_REMOVEMAPPING * - add map_alignment to fuse_init_out, add FUSE_MAP_ALIGNMENT flag + * - add FUSE_HANDLE_KILLPRIV_V2 */ #ifndef _LINUX_FUSE_H @@ -316,6 +317,11 @@ struct fuse_file_lock { * FUSE_MAP_ALIGNMENT: init_out.map_alignment contains log2(byte alignment) for * foffset and moffset fields in struct * fuse_setupmapping_out and fuse_removemapping_one. + * FUSE_HANDLE_KILLPRIV_V2: fs kills suid/sgid/cap on write/chown/trunc. + * Upon write/truncate suid/sgid is only killed if caller + * does not have CAP_FSETID. Additionally upon + * write/truncate sgid is killed only if file has group + * execute permission. (Same as Linux VFS behavior). */ #define FUSE_ASYNC_READ (1 << 0) #define FUSE_POSIX_LOCKS (1 << 1) @@ -344,6 +350,7 @@ struct fuse_file_lock { #define FUSE_NO_OPENDIR_SUPPORT (1 << 24) #define FUSE_EXPLICIT_INVAL_DATA (1 << 25) #define FUSE_MAP_ALIGNMENT (1 << 26) +#define FUSE_HANDLE_KILLPRIV_V2 (1 << 27) /** * CUSE INIT request/reply flags -- 2.25.4