From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from s3.sipsolutions.net ([144.76.63.242]:53052 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752481AbdLEQe0 (ORCPT ); Tue, 5 Dec 2017 11:34:26 -0500 Message-ID: <1512491661.26976.19.camel@sipsolutions.net> (sfid-20171205_173438_593931_3BE74C28) Subject: Re: [PATCH net 1/2] netlink: add NLA_U8_BUGGY attribute type From: Johannes Berg To: David Miller Cc: linux-wireless@vger.kernel.org, netdev@vger.kernel.org, j@w1.fi, dsahern@gmail.com Date: Tue, 05 Dec 2017 17:34:21 +0100 In-Reply-To: <20171205.113145.172521292247335321.davem@davemloft.net> References: <20171202202332.10205-1-johannes@sipsolutions.net> <20171205.113145.172521292247335321.davem@davemloft.net> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Tue, 2017-12-05 at 11:31 -0500, David Miller wrote: > > > We could try to fix up the big endian problem here, but we > > don't know *how* userspace misbehaved - if using nla_put_u32 > > then we could, but we also found a debug tool (which we'll > > ignore for the purposes of this regression) that was putting > > the padding into the length. > We're stuck with this thing forever... I'd like to consider other > options. > > I've seen this problem at least one time before, therefore I > suggest when we see a U8 attribute with a U32's length: > > 1) We access it as a u32, this takes care of all endianness > issues. Possible, but as I said above, I've seen at least one tool (a debug only script) now that will actually emit a U8 followed by 3 bytes of padding to make it netlink-aligned, but set the length to 4. That would be broken by making this change. I'm not saying this is bad - but there are different levels of compatibility and I'd probably go for "bug compatibility" here rather than "fix-it-up compatibility". Your call, ultimately - I've already fixed the tool I had found :-) > 2) We emit a warning so that the app gets fixes. For sure. johannes