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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18BC5C433EF for ; Tue, 10 May 2022 20:10:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4CC076B0072; Tue, 10 May 2022 16:10:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 455036B0073; Tue, 10 May 2022 16:10:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2CD5A6B0074; Tue, 10 May 2022 16:10:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 1A2186B0072 for ; Tue, 10 May 2022 16:10:51 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id E0B7121D42 for ; Tue, 10 May 2022 20:10:50 +0000 (UTC) X-FDA: 79450926660.16.66E6FA1 Received: from gnuweeb.org (gnuweeb.org [51.81.211.47]) by imf13.hostedemail.com (Postfix) with ESMTP id 62DD8200A2 for ; Tue, 10 May 2022 20:10:33 +0000 (UTC) Received: from [192.168.88.87] (unknown [180.242.99.67]) by gnuweeb.org (Postfix) with ESMTPSA id 85BFE7F610; Tue, 10 May 2022 20:10:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gnuweeb.org; s=default; t=1652213448; bh=xGbGpRh0CXRIes2avgyarli9Rp73tR9kYCMcxSyKOGY=; h=Date:To:Cc:References:From:Subject:In-Reply-To:From; b=Y71uOwEP1OuzgfBJxJAcbh3DjOMp7w2q8B0ZlPEpb0WGBpLN/0UGzZU6oKjaT4vT+ NaE/pD4g8oxs1aCCjbG8mKILd0KY01Oo0rTCzXVzL50WWYyZlhYs+CQFqYcgMt6/UE nkFhdPf6WH8g4x5XFZUkdmYEyAI1Hfp6JiEWVQ+OMA5UddcvK3TWlBI6OA0s57hEuJ AyXljU0N5gCxu3KHObvJz+NhWrb/slPVsmRthyrfkzprlKG4IRuEukoArktZtYZHZ/ hGyVVp9ZPzqFgUD0pj45XCMJf8LJFk3WQ69vYnlJdiMuCOwha46/0ytHQs1qvQSTS9 DJJ4LQIjvuApA== Message-ID: <435b5f7a-fcbd-f7ae-b66f-670e5997aa1b@gnuweeb.org> Date: Wed, 11 May 2022 03:10:31 +0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Content-Language: en-US To: cgel.zte@gmail.com Cc: Andrew Morton , 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 References: <20220507105926.d4423601230f698b0f5228d1@linux-foundation.org> <20220508092710.930126-1-xu.xin16@zte.com.cn> From: Ammar Faizi Subject: Re: [PATCH v5] mm/ksm: introduce ksm_force for each process In-Reply-To: <20220508092710.930126-1-xu.xin16@zte.com.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 62DD8200A2 X-Stat-Signature: q3jj9udhrdmc943hofpaeuomn5bpwkni Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=gnuweeb.org header.s=default header.b=Y71uOwEP; spf=pass (imf13.hostedemail.com: domain of ammarfaizi2@gnuweeb.org designates 51.81.211.47 as permitted sender) smtp.mailfrom=ammarfaizi2@gnuweeb.org; dmarc=pass (policy=none) header.from=gnuweeb.org X-HE-Tag: 1652213433-578833 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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'; ``` -- Ammar Faizi