From patchwork Thu Jun 28 16:40:13 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 10494817 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 0387860325 for ; Thu, 28 Jun 2018 19:06:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 082D62A414 for ; Thu, 28 Jun 2018 19:06:13 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id F04C32A42D; Thu, 28 Jun 2018 19:06:12 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 911A92A414 for ; Thu, 28 Jun 2018 19:06:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968022AbeF1TDv (ORCPT ); Thu, 28 Jun 2018 15:03:51 -0400 Received: from mx2.suse.de ([195.135.220.15]:40130 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S968003AbeF1TDs (ORCPT ); Thu, 28 Jun 2018 15:03:48 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C7688AD9E; Thu, 28 Jun 2018 19:03:44 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 042671E3C27; Thu, 28 Jun 2018 18:40:32 +0200 (CEST) From: Jan Kara To: linux-audit@redhat.com Cc: Paul Moore , , Al Viro , Richard Guy Briggs , Jan Kara Subject: [PATCH 5/6] audit: Make hash table insertion safe against concurrent lookups Date: Thu, 28 Jun 2018 18:40:13 +0200 Message-Id: <20180628164014.4925-6-jack@suse.cz> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20180628164014.4925-1-jack@suse.cz> References: <20180628164014.4925-1-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently, the audit tree code does not make sure that when a chunk in inserted into the hash table, it is fully initialized. So in theory (in practice only on DEC Alpha) a user of RCU lookup could see uninitialized structure in the hash table and crash. Add appropriate barriers between initialization of the structure and its insertion into hash table. Signed-off-by: Jan Kara --- kernel/audit_tree.c | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c index 89ad8857a578..46cc6d046c75 100644 --- a/kernel/audit_tree.c +++ b/kernel/audit_tree.c @@ -198,7 +198,11 @@ struct audit_chunk *audit_tree_lookup(const struct inode *inode) struct audit_chunk *p; list_for_each_entry_rcu(p, list, hash) { - if (p->key == key) { + /* + * We use a data dependency barrier in READ_ONCE() to make sure + * the chunk we see is fully initialized. + */ + if (READ_ONCE(p->key) == key) { atomic_long_inc(&p->refs); return p; } @@ -303,9 +307,15 @@ static void untag_chunk(struct node *p) list_replace_init(&chunk->owners[j].list, &new->owners[i].list); } - list_replace_rcu(&chunk->hash, &new->hash); list_for_each_entry(owner, &new->trees, same_root) owner->root = new; + /* + * Make sure chunk is fully initialized before making it visible in the + * hash. Pairs with a data dependency barrier in READ_ONCE() in + * audit_tree_lookup(). + */ + smp_wmb(); + list_replace_rcu(&chunk->hash, &new->hash); spin_unlock(&hash_lock); fsnotify_detach_mark(entry); mutex_unlock(&entry->group->mark_mutex); @@ -367,6 +377,12 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree) list_add(&tree->same_root, &chunk->trees); } chunk->key = inode_to_key(inode); + /* + * Make sure chunk is fully initialized before making it visible in the + * hash. Pairs with a data dependency barrier in READ_ONCE() in + * audit_tree_lookup(). + */ + smp_wmb(); insert_hash(chunk); spin_unlock(&hash_lock); mutex_unlock(&audit_tree_group->mark_mutex); @@ -458,7 +474,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree) p->owner = tree; get_tree(tree); list_add(&p->list, &tree->chunks); - list_replace_rcu(&old->hash, &chunk->hash); list_for_each_entry(owner, &chunk->trees, same_root) owner->root = chunk; old->dead = 1; @@ -466,6 +481,13 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree) tree->root = chunk; list_add(&tree->same_root, &chunk->trees); } + /* + * Make sure chunk is fully initialized before making it visible in the + * hash. Pairs with a data dependency barrier in READ_ONCE() in + * audit_tree_lookup(). + */ + smp_wmb(); + list_replace_rcu(&old->hash, &chunk->hash); spin_unlock(&hash_lock); fsnotify_detach_mark(old_entry); mutex_unlock(&audit_tree_group->mark_mutex);