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=-14.8 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_BLACK 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 94A18C432BE for ; Tue, 3 Aug 2021 11:16:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7766661040 for ; Tue, 3 Aug 2021 11:16:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235502AbhHCLQg (ORCPT ); Tue, 3 Aug 2021 07:16:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:51250 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235329AbhHCLQf (ORCPT ); Tue, 3 Aug 2021 07:16:35 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7B14A61040; Tue, 3 Aug 2021 11:16:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1627989383; bh=irsKls81jNM6jGZibRYCKH0dVnnI1L1OshG9DEuboV8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PpUOvRNBM7tUwfU7zMqz8mkVQmcP5+8ie0RX2MW/3LqeWRaeSHmQli4vav9yCLrPV R2bHrVQXWLXmG8Bak60QArsN42gjH3mX2CzGj6wt8YScfe0baiM7UH75qbXpkbQYx/ P/CxNxc4YxA1tU0BaDb68GGY0m6GwHjnLxmd4hEU= Date: Tue, 3 Aug 2021 13:16:18 +0200 From: Greg KH To: Alexey Kardashevskiy Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini Subject: Re: [RFC PATCH kernel] KVM: Stop leaking memory in debugfs Message-ID: References: <20210730043217.953384-1-aik@ozlabs.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210730043217.953384-1-aik@ozlabs.ru> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 30, 2021 at 02:32:17PM +1000, Alexey Kardashevskiy wrote: > The debugfs folder name is made of a supposedly unique pair of > the process pid and a VM fd. However it is possible to get a race here > which manifests in these messages: > > [ 471.846235] debugfs: Directory '20245-4' with parent 'kvm' already present! > > debugfs_create_dir() returns an error which is handled correctly > everywhere except kvm_create_vm_debugfs() where the code allocates > stat data structs and overwrites the older values regardless. > > Spotted by syzkaller. This slow memory leak produces way too many > OOM reports. > > Signed-off-by: Alexey Kardashevskiy > --- > > I am pretty sure we better fix the race but I am not quite sure what > lock is appropriate here, ideas? > > --- > virt/kvm/kvm_main.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 986959833d70..89496fd8127a 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -904,6 +904,10 @@ static int kvm_create_vm_debugfs(struct kvm *kvm, int fd) > > snprintf(dir_name, sizeof(dir_name), "%d-%d", task_pid_nr(current), fd); > kvm->debugfs_dentry = debugfs_create_dir(dir_name, kvm_debugfs_dir); > + if (IS_ERR_OR_NULL(kvm->debugfs_dentry)) { > + pr_err("Failed to create %s\n", dir_name); > + return 0; > + } It should not matter if you fail a debugfs call at all. If there is a larger race at work here, please fix that root cause, do not paper over it by attempting to have debugfs catch the issue for you. thanks, greg k-h