[{"id":2137749,"web_url":"http://patchwork.ozlabs.org/comment/2137749/","msgid":"","list_archive_url":null,"date":"2019-04-02T22:40:47","subject":"Re: [Qemu-devel] [PULL 10/14] nbd/client: Reject inaccessible tail\n\tof inconsistent server","submitter":{"id":6591,"url":"http://patchwork.ozlabs.org/api/people/6591/","name":"Eric Blake","email":"eblake@redhat.com"},"content":"On 4/1/19 9:08 AM, Eric Blake wrote:\n> The NBD spec suggests that a server should never advertise a size\n> inconsistent with its minimum block alignment, as that tail is\n> effectively inaccessible to a compliant client obeying those block\n> constraints. Since we have a habit of rounding up rather than\n> truncating, to avoid losing the last few bytes of user input, and we\n> cannot access the tail when the server advertises bogus block sizing,\n> abort the connection to alert the server to fix their bug. And\n> rejecting such servers matches what we already did for a min_block\n> that was not a power of 2 or which was larger than max_block.\n> \n> Does not impact either qemu (which always sends properly aligned\n> sizes) or nbdkit (which does not send minimum block requirements yet);\n> so this is mostly aimed at new NBD server implementations, and ensures\n> that the rest of our code can assume the size is aligned.\n> \n> Signed-off-by: Eric Blake \n> Message-Id: <20190330155704.24191-1-eblake@redhat.com>\n> Reviewed-by: Vladimir Sementsov-Ogievskiy \n> ---\n> nbd/client.c | 8 ++++++++\n> 1 file changed, 8 insertions(+)\n> \n> diff --git a/nbd/client.c b/nbd/client.c\n> index de7da48246b..427980bdd22 100644\n> --- a/nbd/client.c\n> +++ b/nbd/client.c\n> @@ -426,6 +426,14 @@ static int nbd_opt_info_or_go(QIOChannel *ioc, uint32_t opt,\n> nbd_send_opt_abort(ioc);\n> return -1;\n> }\n> + if (info->min_block &&\n> + !QEMU_IS_ALIGNED(info->size, info->min_block)) {\n> + error_setg(errp, \"export size %\" PRIu64 \"is not multiple of \"\n\nMissing a space in the error message. If I have any other patches worthy\nof an -rc3 pull request, I'll do the obvious fix then.","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@bilbo.ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=pass (mailfrom) smtp.mailfrom=nongnu.org\n\t(client-ip=209.51.188.17; helo=lists.gnu.org;\n\tenvelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n\treceiver=)","ozlabs.org;\n\tdmarc=fail (p=none dis=none) header.from=redhat.com"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))\n\t(No client certificate requested)\n\tby ozlabs.org (Postfix) with ESMTPS id 44Ykhr4Twlz9sP7\n\tfor ;\n\tWed, 3 Apr 2019 09:41:28 +1100 (AEDT)","from localhost ([127.0.0.1]:46240 helo=lists.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.71) (envelope-from\n\t)\n\tid 1hBS5t-0004gZ-Or\n\tfor incoming@patchwork.ozlabs.org; Tue, 02 Apr 2019 18:41:25 -0400","from eggs.gnu.org ([209.51.188.92]:58447)\n\tby lists.gnu.org with esmtp (Exim 4.71)\n\t(envelope-from ) id 1hBS5O-0004eJ-Km\n\tfor qemu-devel@nongnu.org; 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