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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 55CE2C43457 for ; Fri, 9 Oct 2020 07:45:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 136282227E for ; Fri, 9 Oct 2020 07:45:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732251AbgJIHpq (ORCPT ); Fri, 9 Oct 2020 03:45:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731740AbgJIHpq (ORCPT ); Fri, 9 Oct 2020 03:45:46 -0400 Received: from sipsolutions.net (s3.sipsolutions.net [IPv6:2a01:4f8:191:4433::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 71F86C0613D2; Fri, 9 Oct 2020 00:45:46 -0700 (PDT) Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.94) (envelope-from ) id 1kQn5j-0028Ss-3l; Fri, 09 Oct 2020 09:45:27 +0200 Message-ID: Subject: Re: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used From: Johannes Berg To: Nicolai Stange Cc: David Laight , 'Taehee Yoo' , "davem@davemloft.net" , "kuba@kernel.org" , "netdev@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "wil6210@qti.qualcomm.com" , "brcm80211-dev-list@cypress.com" , "b43-dev@lists.infradead.org" , "linux-bluetooth@vger.kernel.org" Date: Fri, 09 Oct 2020 09:45:20 +0200 In-Reply-To: <87v9fkgf4i.fsf@suse.de> References: <20201008155048.17679-1-ap420073@gmail.com> <1cbb69d83188424e99b2d2482848ae64@AcuMS.aculab.com> <62f6c2bd11ed8b25c1cd4462ebc6db870adc4229.camel@sipsolutions.net> <87v9fkgf4i.fsf@suse.de> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-1.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-bluetooth@vger.kernel.org On Fri, 2020-10-09 at 07:09 +0200, Nicolai Stange wrote: > Johannes Berg writes: > > > On Thu, 2020-10-08 at 15:59 +0000, David Laight wrote: > > > From: Taehee Yoo > > > > Sent: 08 October 2020 16:49 > > > > > > > > When debugfs file is opened, its module should not be removed until > > > > it's closed. > > > > Because debugfs internally uses the module's data. > > > > So, it could access freed memory. > > > > > > > > In order to avoid panic, it just sets .owner to THIS_MODULE. > > > > So that all modules will be held when its debugfs file is opened. > > > > > > Can't you fix it in common code? > > Probably not: it's the call to ->release() that's faulting in the Oops > quoted in the cover letter and that one can't be protected by the > core debugfs code, unfortunately. > > There's a comment in full_proxy_release(), which reads as > > /* > * We must not protect this against removal races here: the > * original releaser should be called unconditionally in order > * not to leak any resources. Releasers must not assume that > * ->i_private is still being meaningful here. > */ Yeah, found that too now :-) > > Yeah I was just wondering that too - weren't the proxy_fops even already > > intended to fix this? > > No, as far as file_operations are concerned, the proxy fops's intent was > only to ensure that the memory the file_operations' ->owner resides in > is still valid so that try_module_get() won't splat at file open > (c.f. [1]). Right. > You're right that the default "full" proxy fops do prevent all > file_operations but ->release() from getting invoked on removed files, > but the motivation had not been to protect the file_operations > themselves, but accesses to any stale data associated with removed files > ([2]). :) I actually got this to work in a crazy way, I'll send something out but I'm sure it's a better idea to add the .owner everywhere, but please let's do it in fewer than hundreds of patches :-) johannes