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 C0C6DC77B73 for ; Mon, 5 Jun 2023 15:14:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234676AbjFEPOX (ORCPT ); Mon, 5 Jun 2023 11:14:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234817AbjFEPNp (ORCPT ); Mon, 5 Jun 2023 11:13:45 -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 637A01A7 for ; Mon, 5 Jun 2023 08:12:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685977919; 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=7+4neYa+KPrHcno9XIjF3OujcOMhzN8ihQFE0Ns9n7U=; b=caqN73YA+JRAiX+89yLx32ggRo6f8KDLIu6Rh1xMbnmG2iEEnzFE5J//JmSrNs5VzwJzde Jg0b6py4USvnfGfWuvaT7r5IJDPbWfPzhItfptD78baT4imoQNkm9q1xFsmfEO71GaYtJU QCn1EaNlDDAukUiHc0WMuZdGxaVIkN8= 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-549-7F3PerAVOMir1dYQzXhJMg-1; Mon, 05 Jun 2023 11:11:55 -0400 X-MC-Unique: 7F3PerAVOMir1dYQzXhJMg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id F28091034AAA; Mon, 5 Jun 2023 15:10:59 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id D0FDC2166B25; Mon, 5 Jun 2023 15:10:57 +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: References: <20230605124600.1722160-1-dhowells@redhat.com> <20230605124600.1722160-4-dhowells@redhat.com> To: Simon Horman Cc: dhowells@redhat.com, netdev@vger.kernel.org, Linus Torvalds , Chuck Lever , Boris Pismenny , John Fastabend , Jakub Kicinski , "David S. Miller" , Eric Dumazet , Paolo Abeni , Willem de Bruijn , David Ahern , Matthew Wilcox , Jens Axboe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v4 03/11] splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1729073.1685977857.1@warthog.procyon.org.uk> Date: Mon, 05 Jun 2023 16:10:57 +0100 Message-ID: <1729074.1685977857@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Simon Horman wrote: > I'm assuming the answer is that this cannot occur, > but I thought I should mention this anyway. > > If the initial value of len is 0 (or less). > ... > > + return spliced ?: ret; > > Then ret will be used uninitialised here. len shouldn't be <0 as it's size_t. I don't think it should be possible to get there with len==0 - at least from userspace. sys_splice() returns immediately and sys_sendfile() either splices to a pipe or goes via splice_direct_to_actor() will just drop straight out. But there are kernel users - nfsd for example - but I don't know if they would splice directly to a socket. That said, it's probably worth preclearing ret just to be sure. David