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 6032EC433FE for ; Tue, 10 May 2022 20:30:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232825AbiEJUaX (ORCPT ); Tue, 10 May 2022 16:30:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229884AbiEJUaV (ORCPT ); Tue, 10 May 2022 16:30:21 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E5E4393F5; Tue, 10 May 2022 13:30:20 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 36C01B81E1D; Tue, 10 May 2022 20:30:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 81084C385CA; Tue, 10 May 2022 20:30:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1652214618; bh=iEm7x6KjhRExhpq8F0JTOjT9f0YF/VsiFX+gYeNlJK0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=qnY0IAokRE1n24DouxgKQ/dIlTNTA/skbjaNu0JimqWU696PDSQa5aznRCubtNuQr +hyAhNTkUT6YnJZMQrne3P8Wvp8+Hh0P/3UPvBr79RmcJSbWWQpKi+OXIB05k9Yr/s UydUk+T0xCHaGO+tzGOxcDoIaAsbYX/8OsSsyCcQ= Date: Tue, 10 May 2022 13:30:16 -0700 From: Andrew Morton To: Ammar Faizi Cc: cgel.zte@gmail.com, Kees Cook , Matthew Wilcox , Yang Yang , Ran Xiaokai , Yunkai Zhang , xu xin , wangyong , Linux MM Mailing List , Linux fsdevel Mailing List , Linux Kernel Mailing List Subject: Re: [PATCH v5] mm/ksm: introduce ksm_force for each process Message-Id: <20220510133016.9feff1aeec1a7a9ae137a8c3@linux-foundation.org> In-Reply-To: <435b5f7a-fcbd-f7ae-b66f-670e5997aa1b@gnuweeb.org> References: <20220507105926.d4423601230f698b0f5228d1@linux-foundation.org> <20220508092710.930126-1-xu.xin16@zte.com.cn> <435b5f7a-fcbd-f7ae-b66f-670e5997aa1b@gnuweeb.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, 11 May 2022 03:10:31 +0700 Ammar Faizi wrote: > On 5/8/22 4:27 PM, cgel.zte@gmail.com wrote: > > +static ssize_t ksm_force_write(struct file *file, const char __user *buf, > > + size_t count, loff_t *ppos) > > +{ > > + struct task_struct *task; > > + struct mm_struct *mm; > > + char buffer[PROC_NUMBUF]; > > + int force; > > + int err = 0; > > + > > + memset(buffer, 0, sizeof(buffer)); > > + if (count > sizeof(buffer) - 1) > > + count = sizeof(buffer) - 1; > > + if (copy_from_user(buffer, buf, count)) { > > + err = -EFAULT; > > + goto out_return; > > + } > > This one looks like over-zeroing to me. You don't need to zero > all elements in the array. You're going to overwrite it with > `copy_from_user()` anyway. > > Just zero the last potentially useful element by using @count > as the index. It can be like this: > > ``` > char buffer[PROC_NUMBUF]; > > if (count > sizeof(buffer) - 1) > count = sizeof(buffer) - 1; > if (copy_from_user(buffer, buf, count)) > return -EFAULT; > buffer[count] = '\0'; > ``` Use strncpy_from_user()? Can this code use proc_dointvec_minmax() or similar?