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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 26D11C43142 for ; Thu, 2 Aug 2018 04:59:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC4AB208D8 for ; Thu, 2 Aug 2018 04:59:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC4AB208D8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codewreck.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727495AbeHBGsZ (ORCPT ); Thu, 2 Aug 2018 02:48:25 -0400 Received: from nautica.notk.org ([91.121.71.147]:50752 "EHLO nautica.notk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727223AbeHBGsZ (ORCPT ); Thu, 2 Aug 2018 02:48:25 -0400 Received: by nautica.notk.org (Postfix, from userid 1001) id BF190C009; Thu, 2 Aug 2018 06:59:06 +0200 (CEST) Date: Thu, 2 Aug 2018 06:58:51 +0200 From: Dominique Martinet To: v9fs-developer@lists.sourceforge.net Cc: Dominique Martinet , linux-kernel@vger.kernel.org, Matthew Wilcox , Greg Kurz , linux-fsdevel@vger.kernel.org Subject: Re: [V9fs-developer] [PATCH v2 2/2] net/9p: add a per-client fcall kmem_cache Message-ID: <20180802045851.GA15564@nautica> References: <1532943263-24378-1-git-send-email-asmadeus@codewreck.org> <1533177452-2165-1-git-send-email-asmadeus@codewreck.org> <1533177452-2165-2-git-send-email-asmadeus@codewreck.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1533177452-2165-2-git-send-email-asmadeus@codewreck.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dominique Martinet wrote on Thu, Aug 02, 2018: > [...] > + clnt->fcall_cache = kmem_cache_create("9p-fcall-cache", clnt->msize, > + 0, 0, NULL); Well, my gut feeling that I'd need a v3 was right, after a bit more time testing (slightly different setup), I got this warning: Bad or missing usercopy whitelist? Kernel memory overwrite attempt detected to SLUB object '9p-fcall-cache' (offset 23, size 55078)! So this kmem_cache_create needs to change to kmem_cache_create_usercopy, but I'm not sure how to best specify the range -- this warning was about writing data to the buffer so a TWRITE: size[4] Twrite tag[2] fid[4] offset[8] count[4] data[count] (the data[count] part comes from user - this matches 4+1+2+4+8+4 = 23) Similarily RREAD has data that can be copied to userspace, which has a similar check: size[4] Rread tag[2] count[4] data[count] So I could hardcode offset = 4+1+2+4=11, usercopy size = msize - 11... We have some P9_*HDR*SZ macros but none are really appropriate: --- /* ample room for Twrite/Rread header */ #define P9_IOHDRSZ 24 /* Room for readdir header */ #define P9_READDIRHDRSZ 24 /* size of header for zero copy read/write */ #define P9_ZC_HDR_SZ 4096 --- It's actually been bugging me for a while that I see hardcoded '7's for 9p main header size (len + msg type + tag) everywhere, I could add a first P9_HDRSZ of 7 and use that + 4? -- Dominique