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 X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 41504C55181 for ; Wed, 22 Apr 2020 06:09:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27C41206D6 for ; Wed, 22 Apr 2020 06:09:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726400AbgDVGJ0 (ORCPT ); Wed, 22 Apr 2020 02:09:26 -0400 Received: from verein.lst.de ([213.95.11.211]:50333 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbgDVGJ0 (ORCPT ); Wed, 22 Apr 2020 02:09:26 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 113CA68C4E; Wed, 22 Apr 2020 08:09:23 +0200 (CEST) Date: Wed, 22 Apr 2020 08:09:22 +0200 From: Christoph Hellwig To: Al Viro Cc: Christoph Hellwig , Kees Cook , Iurii Zaikin , Alexei Starovoitov , Daniel Borkmann , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH 5/5] sysctl: pass kernel pointers to ->proc_handler Message-ID: <20200422060922.GA22775@lst.de> References: <20200421171539.288622-1-hch@lst.de> <20200421171539.288622-6-hch@lst.de> <20200421191615.GE23230@ZenIV.linux.org.uk> <20200422024626.GI23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422024626.GI23230@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Apr 22, 2020 at 03:46:26AM +0100, Al Viro wrote: > > Better allocate count + 1 bytes here, that way a lot of insanity in the > > instances can be simply converted to snprintf(). Yes, I know it'll bring > > the Church Of Avoiding The Abomination Of Sprintf out of the woodwork, > > but... > > FWIW, consider e.g. net/sunrpc/sysctl.c: > > Nevermind that the read side should be simply > int err = proc_douintvec(table, write, buffer, lenp, ppos); > /* Display the RPC tasks on writing to rpc_debug */ > if (!err && strcmp(table->procname, "rpc_debug") == 0) > rpc_show_tasks(&init_net); > return err; > the write side would become > len = snprintf(buffer, *lenp + 1, "0x%04x\n", > *(unsigned int *)table->data); > if (len > *lenp) > len = *lenp; > *lenp -= len; > *ppos += len; > return 0; > and I really wonder if lifting the trailing boilerplate into the caller would've > been better. Note that e.g. gems like > if (!first) > err = proc_put_char(&buffer, &left, '\t'); > if (err) > break; > err = proc_put_long(&buffer, &left, lval, neg); > if (err) > break; > are due to lack of snprintf-to-user; now, lose the "to user" part and we suddenly > can be rid of that stuff... That sounds pretty sensible, but can we do that as an extra step? That is in merge window N just move to passing kernel pointers, check for fall out. In merge window N + 1 start allocatin the extra byte and switch at least the common helpers for snprintf?