From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbdKMSUZ (ORCPT ); Mon, 13 Nov 2017 13:20:25 -0500 Received: from dougal.metanate.com ([90.155.101.14]:1148 "EHLO metanate.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752506AbdKMSUY (ORCPT ); Mon, 13 Nov 2017 13:20:24 -0500 Date: Mon, 13 Nov 2017 18:19:54 +0000 From: John Keeping To: Felipe Balbi Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Vincent Pelletier , Jim Lin Subject: Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT Message-ID: <20171113181954.41d47cb8.john@metanate.com> In-Reply-To: <877euue99q.fsf@linux.intel.com> References: <20171109163429.8697-1-john@metanate.com> <874lq2zaag.fsf@linux.intel.com> <20171110183408.4fc19913.john@metanate.com> <877euue99q.fsf@linux.intel.com> Organization: Metanate Ltd X-Mailer: Claws Mail 3.15.1-dirty (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 13 Nov 2017 12:57:21 +0200, Felipe Balbi wrote: > Good point. Then how about we just force the value to 1 in f_fs.c and > remove the check? That seems reasonable. Something like this? -- >8 -- Subject: [PATCH] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT The specification says that the Reserved1 field in OS_DESC_EXT_COMPAT must have the value "1", but when this feature was first implemented we rejected any non-zero values. This was adjusted to accept all non-zero values (while now rejecting zero) in commit 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT"), but that breaks any userspace programs that worked previously by returning EINVAL when Reserved1 == 0 which was previously the only value that succeeded! If we just set the field to "1" ourselves, both old and new userspace programs continue to work correctly and, as a bonus, old programs are now compliant with the specification without having to fix anything themselves. Fixes: 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT") Cc: stable@vger.kernel.org Signed-off-by: John Keeping --- drivers/usb/gadget/function/f_fs.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 652397eda6d6..520a96e7ef9a 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -2282,9 +2282,18 @@ static int __ffs_data_do_os_desc(enum ffs_os_desc_type type, int i; if (len < sizeof(*d) || - d->bFirstInterfaceNumber >= ffs->interfaces_count || - !d->Reserved1) + d->bFirstInterfaceNumber >= ffs->interfaces_count) return -EINVAL; + if (d->Reserved1 != 1) { + /* + * According to the spec, Reserved1 must be set to 1 + * but older kernels incorrectly rejected non-zero + * values. We fix it here to avoid returning EINVAL + * in response to values we used to accept. + */ + pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n"); + d->Reserved1 = 1; + } for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i) if (d->Reserved2[i]) return -EINVAL; -- 2.15.0