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 Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A042AC4345F for ; Mon, 22 Apr 2024 09:21:04 +0000 (UTC) Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id 2C5D9E66; Mon, 22 Apr 2024 11:20:52 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz 2C5D9E66 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1713777662; bh=T5tRASABoyAmF4/TwmiQdb4aSxJ5IjEe6kgVUHlghnY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-Id: List-Archive:List-Help:List-Owner:List-Post:List-Subscribe: List-Unsubscribe:From; b=NwjEJU/nlZRw4X5agtXCZH5eR+d048Hg/CrzTBqynQMG7ZNduKq2lRcQT2cNNA5rl 25swOACOnE/9KwNB23zEEkDfT0HV6371g8jRZJRs9t+FUWGsE3pw8bdfupneZIt9XC 3J5UdDO6OtuemBr8l54T05ROgGv6xFRfnnoL/uzM= Received: by alsa1.perex.cz (Postfix, from userid 50401) id 0963AF8057C; Mon, 22 Apr 2024 11:20:30 +0200 (CEST) Received: from mailman-core.alsa-project.org (mailman-core.alsa-project.org [10.254.200.10]) by alsa1.perex.cz (Postfix) with ESMTP id A6D46F805A0; Mon, 22 Apr 2024 11:20:30 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 71D44F802E8; Mon, 22 Apr 2024 11:20:26 +0200 (CEST) Received: from bmailout2.hostsharing.net (bmailout2.hostsharing.net [83.223.78.240]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id C5AB4F800B5 for ; Mon, 22 Apr 2024 11:20:16 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz C5AB4F800B5 Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by bmailout2.hostsharing.net (Postfix) with ESMTPS id 2EF4A280108A8; Mon, 22 Apr 2024 11:20:16 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 03FB34D34A; Mon, 22 Apr 2024 11:20:15 +0200 (CEST) Date: Mon, 22 Apr 2024 11:20:15 +0200 From: Lukas Wunner To: Dan Williams Cc: gregkh@linuxfoundation.org, Pierre-Louis Bossart , Marc Herbert , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-coco@lists.linux.dev, alsa-devel@alsa-project.org Subject: Re: [PATCH 1/3] sysfs: Fix crash on empty group attributes array Message-ID: References: <170863444851.1479840.10249410842428140526.stgit@dwillia2-xfh.jf.intel.com> <170863445442.1479840.1818801787239831650.stgit@dwillia2-xfh.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <170863445442.1479840.1818801787239831650.stgit@dwillia2-xfh.jf.intel.com> Message-ID-Hash: QHNSZCUPAE226SPNYO2SRAJZA6OSWFTN X-Message-ID-Hash: QHNSZCUPAE226SPNYO2SRAJZA6OSWFTN X-MailFrom: foo00@h08.hostsharing.net X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-alsa-devel.alsa-project.org-0; header-match-alsa-devel.alsa-project.org-1; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.9 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, Feb 22, 2024 at 12:40:54PM -0800, Dan Williams wrote: > It turns out that arch/x86/events/intel/core.c makes use of "empty" > attributes. > > static struct attribute *empty_attrs; > > __init int intel_pmu_init(void) > { > struct attribute **extra_skl_attr = &empty_attrs; > struct attribute **extra_attr = &empty_attrs; > struct attribute **td_attr = &empty_attrs; > struct attribute **mem_attr = &empty_attrs; > struct attribute **tsx_attr = &empty_attrs; > ... > > That breaks the assumption __first_visible() that expects that if > grp->attrs is set then grp->attrs[0] must also be set and results in > backtraces like: > > BUG: kernel NULL pointer dereference, address: 00rnel mode > #PF: error_code(0x0000) - not-present ] PREEMPT SMP NOPTI > CPU: 1 PID: 1 Comm: swapper/IP: 0010:exra_is_visible+0x14/0x20 > ? exc_page_fault+0x68/0x190 > internal_create_groups+0x42/0xa0 > pmu_dev_alloc+0xc0/0xe0 > perf_event_sysfs_init+0x580000000000 ]--- > RIP: 0010:exra_is_visible+0x14/0 > > Check for non-empty attributes array before calling is_visible(). [...] > --- a/fs/sysfs/group.c > +++ b/fs/sysfs/group.c > @@ -33,10 +33,10 @@ static void remove_files(struct kernfs_node *parent, > > static umode_t __first_visible(const struct attribute_group *grp, struct kobject *kobj) > { > - if (grp->attrs && grp->is_visible) > + if (grp->attrs && grp->attrs[0] && grp->is_visible) > return grp->is_visible(kobj, grp->attrs[0], 0); > > - if (grp->bin_attrs && grp->is_bin_visible) > + if (grp->bin_attrs && grp->bin_attrs[0] && grp->is_bin_visible) > return grp->is_bin_visible(kobj, grp->bin_attrs[0], 0); > > return 0; I'm wondering why 0 is returned by default and not SYSFS_GROUP_INVISIBLE. An empty attribute list (containing just the NULL sentinel) will now result in the attribute group being visible as an empty directory. I thought the whole point was to hide such empty directories. Was it a conscious decision to return 0? Did you expect breakage if SYSFS_GROUP_INVISIBLE is returned? Thanks, Lukas