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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 14FD0C433EB for ; Tue, 21 Jul 2020 23:01:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF04B20849 for ; Tue, 21 Jul 2020 23:01:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595372464; bh=HkY2xoW+5h/KPN4NirPSCI6mZ1dMQTytJsLYKF1i9Kk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=kJAGRmpiP/RX5zg3ij9ncd5BYkQHRvPDKKU99jXF2EDtC5qZSa40oSzZi+9NPlf85 f0b5oFgc59JifrjplmufEYfojvogRVAwoSN/67C00+EneRnMDgUvVcArvYlH7Tpab5 2KbOMVFSY0vhqSNbJjFSW6xBzX/5CcbWMPp/OwXw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731334AbgGUXBE (ORCPT ); Tue, 21 Jul 2020 19:01:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:48990 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgGUXBA (ORCPT ); Tue, 21 Jul 2020 19:01:00 -0400 Received: from sol.hsd1.ca.comcast.net (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9616A207BB; Tue, 21 Jul 2020 23:00:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595372459; bh=HkY2xoW+5h/KPN4NirPSCI6mZ1dMQTytJsLYKF1i9Kk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k3Gk9VGnsqGB5y+WMg5lND+8JiNxzRrc4VjLmUb1EIy9UlP7HqQV7CTx+ehe/RuD1 XuaTIIvbwwLc5tFsjkcZoEyxBDu3L+o2yMrmwuMjDcbypkZuUM4Or6eNsG2RGZ5mhI VdEvSYtK16hT7PpUn/1yWdPuPeao//sgvXC/ASxo= From: Eric Biggers To: linux-fscrypt@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: [PATCH 3/5] fscrypt: use smp_load_acquire() for ->s_master_keys Date: Tue, 21 Jul 2020 15:59:18 -0700 Message-Id: <20200721225920.114347-4-ebiggers@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200721225920.114347-1-ebiggers@kernel.org> References: <20200721225920.114347-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-fscrypt-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fscrypt@vger.kernel.org From: Eric Biggers Normally smp_store_release() or cmpxchg_release() is paired with smp_load_acquire(). Sometimes smp_load_acquire() can be replaced with the more lightweight READ_ONCE(). However, for this to be safe, all the published memory must only be accessed in a way that involves the pointer itself. This may not be the case if allocating the object also involves initializing a static or global variable, for example. super_block::s_master_keys is a keyring, which is internal to and is allocated by the keyrings subsystem. By using READ_ONCE() for it, we're relying on internal implementation details of the keyrings subsystem. Remove this fragile assumption by using smp_load_acquire() instead. (Note: I haven't seen any real-world problems here. This change is just fixing the code to be guaranteed correct and less fragile.) Fixes: 22d94f493bfb ("fscrypt: add FS_IOC_ADD_ENCRYPTION_KEY ioctl") Signed-off-by: Eric Biggers --- fs/crypto/keyring.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c index 7f8ac61a20d6..71d56f8e2870 100644 --- a/fs/crypto/keyring.c +++ b/fs/crypto/keyring.c @@ -213,7 +213,11 @@ static int allocate_filesystem_keyring(struct super_block *sb) if (IS_ERR(keyring)) return PTR_ERR(keyring); - /* Pairs with READ_ONCE() in fscrypt_find_master_key() */ + /* + * Pairs with the smp_load_acquire() in fscrypt_find_master_key(). + * I.e., here we publish ->s_master_keys with a RELEASE barrier so that + * concurrent tasks can ACQUIRE it. + */ smp_store_release(&sb->s_master_keys, keyring); return 0; } @@ -234,8 +238,13 @@ struct key *fscrypt_find_master_key(struct super_block *sb, struct key *keyring; char description[FSCRYPT_MK_DESCRIPTION_SIZE]; - /* pairs with smp_store_release() in allocate_filesystem_keyring() */ - keyring = READ_ONCE(sb->s_master_keys); + /* + * Pairs with the smp_store_release() in allocate_filesystem_keyring(). + * I.e., another task can publish ->s_master_keys concurrently, + * executing a RELEASE barrier. We need to use smp_load_acquire() here + * to safely ACQUIRE the memory the other task published. + */ + keyring = smp_load_acquire(&sb->s_master_keys); if (keyring == NULL) return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */ -- 2.27.0