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 1FCC1C0015E for ; Tue, 1 Aug 2023 16:58:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231732AbjHAQ6f (ORCPT ); Tue, 1 Aug 2023 12:58:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231223AbjHAQ6d (ORCPT ); Tue, 1 Aug 2023 12:58:33 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CE41DA for ; Tue, 1 Aug 2023 09:57:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1690909066; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ZKlr7hPRFIg1XM1Mg6RUtTCl8BMjdJxudj9aZC6n25E=; b=f/xJRKlBpiJ3cPJXSjNSd/3N+XvLgdUpel+tGEjdHIqkSnZYJ1NZ5WA9QsN5QLOYDiaHRM KQdCLw+tC5nIYUv9Pc9TYBWIgqMxj8sImXq/fwikRkxYZYV+zVbeBUXzWS8naY5HRhC/3U Xedqg7A/LARjqtpji14pw4u6IFP44Qc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-651-z-DU3XkbPMy31HetIn3hYg-1; Tue, 01 Aug 2023 12:57:44 -0400 X-MC-Unique: z-DU3XkbPMy31HetIn3hYg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 36A678007CE; Tue, 1 Aug 2023 16:57:43 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id 743114024F83; Tue, 1 Aug 2023 16:57:41 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <64c93109c084e_1c5e3529452@willemb.c.googlers.com.notmuch> References: <64c93109c084e_1c5e3529452@willemb.c.googlers.com.notmuch> <1420063.1690904933@warthog.procyon.org.uk> To: Willem de Bruijn Cc: dhowells@redhat.com, netdev@vger.kernel.org, syzbot+f527b971b4bdc8e79f9e@syzkaller.appspotmail.com, bpf@vger.kernel.org, brauner@kernel.org, davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, axboe@kernel.dk, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, syzkaller-bugs@googlegroups.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH net] udp: Fix __ip_append_data()'s handling of MSG_SPLICE_PAGES MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1481563.1690909060.1@warthog.procyon.org.uk> Date: Tue, 01 Aug 2023 17:57:40 +0100 Message-ID: <1481564.1690909060@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Willem de Bruijn wrote: > copy -= -fraggap definitely seems off. You point out that it even can > turn length negative? Yes. See the logging I posted: ==>splice_to_socket() 6630 udp_sendmsg(8,8) __ip_append_data(copy=-1,len=8, mtu=8192 skblen=8189 maxfl=8188) pagedlen 9 = 9 - 0 copy -1 = 9 - 0 - 1 - 9 length 8 -= -1 + 0 Since datalen and transhdrlen cancel, and fraggap is unsigned, if fraggap is non-zero, copy will be negative. > The WARN_ON_ONCE, if it can be reached, will be user triggerable. > Usually for those cases and when there is a viable return with error > path, that is preferable. But if you prefer to taunt syzbot, ok. We > can always remove this later. It shouldn't be possible for length to exceed msg->msg_iter.count (assuming there is a msg) coming from userspace; further, userspace can't directly specify MSG_SPLICE_PAGES. > __ip6_append_data probably needs the same. Good point. The arrangement of the code is a bit different, but I think it's substantially the same in this regard. David