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=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 2B2CEC432BE for ; Tue, 10 Aug 2021 18:05:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 10B9C60232 for ; Tue, 10 Aug 2021 18:05:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237281AbhHJSGL (ORCPT ); Tue, 10 Aug 2021 14:06:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:34378 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238081AbhHJSBv (ORCPT ); Tue, 10 Aug 2021 14:01:51 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 44F36613E6; Tue, 10 Aug 2021 17:47:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1628617641; bh=F5NLuY5cYUC4pSVKKOzoTdT9SeoUIXt3QoWU+t+O2io=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1luMiBm0U1MktrQXSobE30hmYkxIUrzAKW0uoFMrESyms8lOAmTcbBO0wpeqob2ag QtvEEBi4JASrnS1P6g1x3ihyncc81k8Gz+OTCBMWoGyJft2/GuHBkFwauq+EPrWKwO uH/HLngYXHbcZdiVKLMIdfa2fB2er2fM3sLsNnFU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Alexey Kardashevskiy , Paolo Bonzini Subject: [PATCH 5.13 149/175] KVM: Do not leak memory for duplicate debugfs directories Date: Tue, 10 Aug 2021 19:30:57 +0200 Message-Id: <20210810173005.879888740@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210810173000.928681411@linuxfoundation.org> References: <20210810173000.928681411@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paolo Bonzini commit 85cd39af14f498f791d8aab3fbd64cd175787f1a upstream. KVM creates a debugfs directory for each VM in order to store statistics about the virtual machine. The directory name is built from the process pid and a VM fd. While generally unique, it is possible to keep a file descriptor alive in a way that causes duplicate directories, which manifests as these messages: [ 471.846235] debugfs: Directory '20245-4' with parent 'kvm' already present! Even though this should not happen in practice, it is more or less expected in the case of KVM for testcases that call KVM_CREATE_VM and close the resulting file descriptor repeatedly and in parallel. When this happens, debugfs_create_dir() returns an error but kvm_create_vm_debugfs() goes on to allocate stat data structs which are later leaked. The slow memory leak was spotted by syzkaller, where it caused OOM reports. Since the issue only affects debugfs, do a lookup before calling debugfs_create_dir, so that the message is downgraded and rate-limited. While at it, ensure kvm->debugfs_dentry is NULL rather than an error if it is not created. This fixes kvm_destroy_vm_debugfs, which was not checking IS_ERR_OR_NULL correctly. Cc: stable@vger.kernel.org Fixes: 536a6f88c49d ("KVM: Create debugfs dir and stat files for each VM") Reported-by: Alexey Kardashevskiy Suggested-by: Greg Kroah-Hartman Acked-by: Greg Kroah-Hartman Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -845,6 +845,8 @@ static void kvm_destroy_vm_debugfs(struc static int kvm_create_vm_debugfs(struct kvm *kvm, int fd) { + static DEFINE_MUTEX(kvm_debugfs_lock); + struct dentry *dent; char dir_name[ITOA_MAX_LEN * 2]; struct kvm_stat_data *stat_data; struct kvm_stats_debugfs_item *p; @@ -853,8 +855,20 @@ static int kvm_create_vm_debugfs(struct return 0; snprintf(dir_name, sizeof(dir_name), "%d-%d", task_pid_nr(current), fd); - kvm->debugfs_dentry = debugfs_create_dir(dir_name, kvm_debugfs_dir); + mutex_lock(&kvm_debugfs_lock); + dent = debugfs_lookup(dir_name, kvm_debugfs_dir); + if (dent) { + pr_warn_ratelimited("KVM: debugfs: duplicate directory %s\n", dir_name); + dput(dent); + mutex_unlock(&kvm_debugfs_lock); + return 0; + } + dent = debugfs_create_dir(dir_name, kvm_debugfs_dir); + mutex_unlock(&kvm_debugfs_lock); + if (IS_ERR(dent)) + return 0; + kvm->debugfs_dentry = dent; kvm->debugfs_stat_data = kcalloc(kvm_debugfs_num_entries, sizeof(*kvm->debugfs_stat_data), GFP_KERNEL_ACCOUNT); @@ -4993,7 +5007,7 @@ static void kvm_uevent_notify_change(uns } add_uevent_var(env, "PID=%d", kvm->userspace_pid); - if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) { + if (kvm->debugfs_dentry) { char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL_ACCOUNT); if (p) {