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 DABA9C433EF for ; Tue, 26 Apr 2022 11:12:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345831AbiDZLPk (ORCPT ); Tue, 26 Apr 2022 07:15:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349487AbiDZLNx (ORCPT ); Tue, 26 Apr 2022 07:13:53 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C542D45ADC for ; Tue, 26 Apr 2022 04:10:45 -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 sin.source.kernel.org (Postfix) with ESMTPS id 49950CE1A4F for ; Tue, 26 Apr 2022 11:10:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 03865C385A0; Tue, 26 Apr 2022 11:10:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1650971442; bh=PSnB5n9Oy0FIntYg4S3JiHi7XxetpXLfpd8AjK/N1X8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fo6FU028U1Zlx5FJF/QLeOVXx60XRSn2JVhhbZ0B1zdEr7Nmr+5QIwgi7dNF80UXR o3eQbsxKwvsBTKby2gXdqw6i9rrpFh0Z2aWFaJqVRq3bbbPM49i+vtH7fyqKHq/aCU Lxq+FRy9vt9H4aE6ngK5MeyqDictrDLRrbGj+BR0= Date: Tue, 26 Apr 2022 13:10:39 +0200 From: Greg Kroah-Hartman To: Bastien Nocera Cc: Oliver Neukum , Peter Hutterer , linux-usb@vger.kernel.org, Alan Stern , Benjamin Tissoires Subject: Re: [RFC v1] USB: core: add USBDEVFS_REVOKE ioctl Message-ID: References: <1d82343a5987a308ac9bd3f6fd481bc12a608a24.camel@hadess.net> <7def25c7-0870-accc-c689-4d8eef1b7acf@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Tue, Apr 26, 2022 at 12:37:14PM +0200, Bastien Nocera wrote: > On Tue, 2022-04-26 at 12:30 +0200, Greg Kroah-Hartman wrote: > > On Tue, Apr 26, 2022 at 12:07:32PM +0200, Bastien Nocera wrote: > > > On Tue, 2022-04-26 at 10:46 +0200, Oliver Neukum wrote: > > > > > > > > > > > > On 26.04.22 09:21, Greg Kroah-Hartman wrote: > > > > > Yes, but, it's not so simple.  Many people have asked for > > > > > revoke() > > > > > to be > > > > > added as a syscall like is in the BSDs, but the BSDs only allow > > > > > that for > > > > > a very small subset of file descriptor types, and doing it in a > > > > > generic > > > > > fashion seems very difficult (I tried a few years ago and gave > > > > > up, > > > > > but > > > > > my knowledge of the vfs layer is minimal.) > > > > Well, then we should go for the minimalist approach and just > > > > add a hook to VFS. Multiple different ioctl()s are definitely a > > > > bad > > > > idea. > > > > An frevoke() looks much easier to do than one based on paths. > > > > If I understand the issue behind the proposal correctly the > > > > caller > > > > has opened the device. > > > > > > Doesn't look like FreeBSD at least has an frevoke() syscall > > > anymore, it > > > had an FREVOKE flag, which is now a define for the O_VERIFY option > > > which has quite different semantics: > > > https://www.freebsd.org/cgi/man.cgi?sektion=2&query=open > > > > Take a look at this implementation: > >         https://man.openbsd.org/revoke.2 > > > I don't think anyone wants to implement path based syscalls, and again, > it's equivalent to remote closing the fd, not to disabling the access > to the device: > "If the file is a special file for a device which is open, the device > close function is called as if all open references to the file had been > closed." You forgot the sentence before that which is the functionality we want here: Subsequent operations on any such descriptors fail, with the exceptions that a read() from a tty which has been revoked returns a count of zero (end of file), and a close() call will succeed. And don't do it only for a tty device, but for any device that implements it. And yes, we don't want to work off of a path, but a file descriptor: int revoke(int fd); > If there's an implementation done at the VFS level, it should probably > try to steer away from those earlier disparate implementations. Agreed. thanks, greg k-h