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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT 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 17B51C43461 for ; Wed, 14 Apr 2021 13:39:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE4FA611B0 for ; Wed, 14 Apr 2021 13:39:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351443AbhDNNkG (ORCPT ); Wed, 14 Apr 2021 09:40:06 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:16919 "EHLO szxga06-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351422AbhDNNkD (ORCPT ); Wed, 14 Apr 2021 09:40:03 -0400 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga06-in.huawei.com (SkyGuard) with ESMTP id 4FL3SV0hfJzjZSG; Wed, 14 Apr 2021 21:37:46 +0800 (CST) Received: from huawei.com (10.175.127.227) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.498.0; Wed, 14 Apr 2021 21:39:29 +0800 From: Zhang Yi To: CC: , , , , , Subject: [RFC PATCH v2 5/7] ext4: use RCU to protect accessing superblock in blkdev_releasepage() Date: Wed, 14 Apr 2021 21:47:35 +0800 Message-ID: <20210414134737.2366971-6-yi.zhang@huawei.com> X-Mailer: git-send-email 2.25.4 In-Reply-To: <20210414134737.2366971-1-yi.zhang@huawei.com> References: <20210414134737.2366971-1-yi.zhang@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.127.227] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org In blkdev_releasepage() we access the superblock structure directly, it could be raced by umount filesystem on destroy superblock in put_super(), and end up triggering a use after free issue. drop cache umount filesystem bdev_try_to_free_page() get superblock deactivate_locked_super() ... put_super() and free sb by destroy_work access superblock <-- trigger use after free This issue doesn't trigger easily in general because we get page locked when invoking bdev_try_to_free_page(), and when umount filesystem the kill_block_super()->..->kill_bdev()->truncate_inode_pages_range() procedure wait on page unlock, but it's not a guarantee. Fix this race by use RCU to protect superblock in blkdev_releasepage(). Fixes: 87d8fe1ee6b8 ("add releasepage hooks to block devices which can be used by file systems") Reported-by: Jan Kara Signed-off-by: Zhang Yi --- fs/block_dev.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 5ed79a9063f6..cb84f347fb04 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -1734,11 +1734,14 @@ EXPORT_SYMBOL_GPL(blkdev_read_iter); */ static int blkdev_releasepage(struct page *page, gfp_t wait) { - struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super; + struct super_block *super; int ret = 0; + rcu_read_lock(); + super = READ_ONCE(BDEV_I(page->mapping->host)->bdev.bd_super); if (super && super->s_op->bdev_try_to_free_page) ret = super->s_op->bdev_try_to_free_page(super, page, wait); + rcu_read_unlock(); if (!ret) return try_to_free_buffers(page); return 0; -- 2.25.4