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 1440FC433F5 for ; Sat, 29 Jan 2022 20:54:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353205AbiA2UyA (ORCPT ); Sat, 29 Jan 2022 15:54:00 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49215 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353175AbiA2Uxz (ORCPT ); Sat, 29 Jan 2022 15:53:55 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643489635; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=f1x6j7RB7xRENYfNa+FT/BlT6fNQP5UqbN6D/s+vZCU=; b=D8ve9czQ5s39VjA26+8tmFbJG/nE2o4ZUAh5SOloNCZSmd+nDiIu2KXdRMkxXitnIrPizZ 4iw6y9vgZWnA2OtkHo3yg30en0UXqSFn6whrO2LxFq7qQkp3SxFP+pMBYVkzw+NwwoweYN nL7/fjN0V5HLsQWzfXVoGW2Hr9a4lSo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-220-y4KFQNNXPxewucIo98fB5w-1; Sat, 29 Jan 2022 15:53:49 -0500 X-MC-Unique: y4KFQNNXPxewucIo98fB5w-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BF0101006AA0; Sat, 29 Jan 2022 20:53:47 +0000 (UTC) Received: from llong.com (unknown [10.22.16.96]) by smtp.corp.redhat.com (Postfix) with ESMTP id 286535DF3A; Sat, 29 Jan 2022 20:53:46 +0000 (UTC) From: Waiman Long To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Ira Weiny , Rafael Aquini , Waiman Long Subject: [PATCH v2 2/3] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check Date: Sat, 29 Jan 2022 15:53:14 -0500 Message-Id: <20220129205315.478628-3-longman@redhat.com> In-Reply-To: <20220129205315.478628-1-longman@redhat.com> References: <20220129205315.478628-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The snprintf() function can return a length greater than the given input size. That will require a check for buffer overrun after each invocation of snprintf(). scnprintf(), on the other hand, will never return a greater length. By using scnprintf() in selected places, we can avoid some buffer overrun checks except after stack_depot_snprint() and after the last snprintf(). Signed-off-by: Waiman Long --- mm/page_owner.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index 99e360df9465..28dac73e0542 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -338,19 +338,16 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, if (!kbuf) return -ENOMEM; - ret = snprintf(kbuf, count, + ret = scnprintf(kbuf, count, "Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n", page_owner->order, page_owner->gfp_mask, &page_owner->gfp_mask, page_owner->pid, page_owner->ts_nsec, page_owner->free_ts_nsec); - if (ret >= count) - goto err; - /* Print information relevant to grouping pages by mobility */ pageblock_mt = get_pageblock_migratetype(page); page_mt = gfp_migratetype(page_owner->gfp_mask); - ret += snprintf(kbuf + ret, count - ret, + ret += scnprintf(kbuf + ret, count - ret, "PFN %lu type %s Block %lu type %s Flags %pGp\n", pfn, migratetype_names[page_mt], @@ -358,19 +355,14 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn, migratetype_names[pageblock_mt], &page->flags); - if (ret >= count) - goto err; - ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0); if (ret >= count) goto err; if (page_owner->last_migrate_reason != -1) { - ret += snprintf(kbuf + ret, count - ret, + ret += scnprintf(kbuf + ret, count - ret, "Page has been migrated, last migrate reason: %s\n", migrate_reason_names[page_owner->last_migrate_reason]); - if (ret >= count) - goto err; } ret += snprintf(kbuf + ret, count - ret, "\n"); -- 2.27.0