From patchwork Mon Dec 4 03:27:14 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 10089593 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id E4FBC6056E for ; Mon, 4 Dec 2017 03:27:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DC66D28F07 for ; Mon, 4 Dec 2017 03:27:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D081228F0C; Mon, 4 Dec 2017 03:27:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 7A49628F07 for ; Mon, 4 Dec 2017 03:27:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753344AbdLDD11 (ORCPT ); Sun, 3 Dec 2017 22:27:27 -0500 Received: from mx2.suse.de ([195.135.220.15]:53318 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752917AbdLDD11 (ORCPT ); Sun, 3 Dec 2017 22:27:27 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 67821ABEB; Mon, 4 Dec 2017 03:27:25 +0000 (UTC) From: NeilBrown To: Trond Myklebust , Anna.Schumaker@Netapp.com, Al Viro , Andrew Morton , Linus Torvalds Date: Mon, 04 Dec 2017 14:27:14 +1100 Cc: lkml , "linux-nfs\@vger.kernel.org" , linux-fsdevel , Lennart Poettering Subject: [PATCH] fhandle: avoid -EINVAL if requested size is too large. In-Reply-To: <87po7zv62h.fsf@notabene.neil.brown.name> References: <87po7zv62h.fsf@notabene.neil.brown.name> Message-ID: <87k1y3tbot.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Lennart Poettering observes that if the newly increased MAX_HANDLE_SZ is exported to user space, and then used in an application running on an old kernel, name_to_handle_at() will report -EINVAL, which is unhelpful and inconsistent with the documentation. So: 1/ add a comment making it clear that the new value must not be exposed to user-space. 2/ remove the completely unnecessary restriction on the size of buffer provided by the application. Reported-by: Lennart Poettering Signed-off-by: NeilBrown --- This is a followup to the previous fhandle-for-Amazon-EFS patch which adds further refinements. Thanks, NeilBrown fs/fhandle.c | 2 +- include/linux/exportfs.h | 4 ++++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/fhandle.c b/fs/fhandle.c index 0ace128f5d23..30bf1c20e143 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -35,7 +35,7 @@ static long do_sys_name_to_handle(struct path *path, return -EFAULT; if (f_handle.handle_bytes > MAX_HANDLE_SZ) - return -EINVAL; + f_handle.handle_bytes = MAX_HANDLE_SZ; handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes, GFP_KERNEL); diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index e7ab1b071c5e..097704e80c89 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -14,6 +14,10 @@ struct vfsmount; /* Must be larger than NFSv4 file handle, but small * enough for an on-stack allocation. overlayfs doesn't * want this too close to 255. + * NOTE: This value MUST NOT be exported to user-space. + * Applications must only ever see MAX_HANDLE_SZ == 128. + * If they try a larger number on older kernels, they + * will get -EINVAL which will be confusing. */ #define MAX_HANDLE_SZ 200