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 B00F3C19F2B for ; Thu, 28 Jul 2022 01:36:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B4FB6940031; Wed, 27 Jul 2022 21:36:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AFEB1940012; Wed, 27 Jul 2022 21:36:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9C680940031; Wed, 27 Jul 2022 21:36:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 8AFF7940012 for ; Wed, 27 Jul 2022 21:36:55 -0400 (EDT) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 586C9A0D49 for ; Thu, 28 Jul 2022 01:36:55 +0000 (UTC) X-FDA: 79734794790.21.320B014 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf25.hostedemail.com (Postfix) with ESMTP id 6D5A6A0016 for ; Thu, 28 Jul 2022 01:36:54 +0000 (UTC) Received: from dggpeml500025.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LtY8l3lpqzkY1V; Thu, 28 Jul 2022 09:34:15 +0800 (CST) Received: from dggpeml500005.china.huawei.com (7.185.36.59) by dggpeml500025.china.huawei.com (7.185.36.35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 28 Jul 2022 09:36:49 +0800 Received: from [10.174.178.155] (10.174.178.155) by dggpeml500005.china.huawei.com (7.185.36.59) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 28 Jul 2022 09:36:48 +0800 Subject: Re: [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page To: William Kucharski CC: Matthew Wilcox , "dhowells@redhat.com" , "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "zhangxiaoxu5@huawei.com" , "yanaijie@huawei.com" , "vbabka@suse.cz" , "wangkefeng.wang@huawei.com" References: <20220727064621.534528-1-liuyongqiang13@huawei.com> From: Yongqiang Liu Message-ID: <3e80debb-eb34-75ed-6c12-feb072e42546@huawei.com> Date: Thu, 28 Jul 2022 09:36:48 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.155] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpeml500005.china.huawei.com (7.185.36.59) X-CFilter-Loop: Reflected ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=none; spf=pass (imf25.hostedemail.com: domain of liuyongqiang13@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=liuyongqiang13@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658972214; a=rsa-sha256; cv=none; b=0c7HVfFWwoODzmrSogXWRQUMergfSdBI8a0fKepa32hj67TMzq8Rj9VVVancyVrQACbh/n IVc9GRCq1yKz9PMRAjbeE1EPunX78QffaXLKk/Txg82EmDMeWOy5hsHyUOaXQxkPRzLkAR fvJleNRAfMTca8LIYaWkHMOrID6BsPE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658972214; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BevTeyk6xF7+K2lNY6CiuseyUjSjdxNFgEtKCl8Xj8k=; b=41N0ZpbzlbEFZS/LNpiozKzJ2NXoXDL1PdSOX5y7Fc3+AZx27kkHGmOkYX0npbbrZhktwf NgKXKFpSXYCIrE98pg4tCzkwDMe6bQN4KrNdJHAZoU9wmKoL1PL96Umtd2RVORmlYsrkVg 6HVzNjnm9xmjk4DwmqD1VTvXvQAYq+M= X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 6D5A6A0016 Authentication-Results: imf25.hostedemail.com; dkim=none; spf=pass (imf25.hostedemail.com: domain of liuyongqiang13@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=liuyongqiang13@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Stat-Signature: x1tqsrkf31ganiztxs61tnf8a9rixj61 X-Rspam-User: X-HE-Tag: 1658972214-273224 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: Understood, thanks for your explanation :) ÔÚ 2022/7/27 19:40, William Kucharski дµÀ: > This isn't a NULL pointer dereference; returning &(0->page) is completely legal > as was discussed regarding this exact code back in April: > > https://lore.kernel.org/lkml/YmfgqKcMmstgfz+0@casper.infradead.org/ > >> On Jul 27, 2022, at 12:46 AM, Yongqiang Liu wrote: >> >> When __filemap_get_folio() failed and returned NULL, we would >> get a NULL pointer dereference in pagecache_get_page. >> >> Fixes: 3f0c6a07fee6 ("mm/filemap: Add filemap_get_folio") >> Signed-off-by: Yongqiang Liu >> Cc: # 5.16 >> --- >> mm/folio-compat.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/mm/folio-compat.c b/mm/folio-compat.c >> index 20bc15b57d93..7b21393480e0 100644 >> --- a/mm/folio-compat.c >> +++ b/mm/folio-compat.c >> @@ -124,7 +124,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index, >> struct folio *folio; >> >> folio = __filemap_get_folio(mapping, index, fgp_flags, gfp); >> - if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio)) >> + if (!folio) >> + return NULL; >> + if ((fgp_flags & FGP_HEAD) || xa_is_value(folio)) >> return &folio->page; >> return folio_file_page(folio, index); >> } >> -- >> 2.25.1 >> >> > .