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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06E4AC25B0E for ; Fri, 19 Aug 2022 07:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347125AbiHSHlO (ORCPT ); Fri, 19 Aug 2022 03:41:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347105AbiHSHlE (ORCPT ); Fri, 19 Aug 2022 03:41:04 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 395E66171E for ; Fri, 19 Aug 2022 00:41:03 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id E8AEA5CAC7; Fri, 19 Aug 2022 07:41:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1660894861; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qmEmRwbvgXw29M6tJMACSOhRvv5bpX5gPHGr1QrxjWg=; b=N9ULk/nSj5ci61DvtWywUkMT1iE7dIgWi7Gv8PWNun41MurpGppwGzShj+qAkJh5f9AEP2 FjVzllqP6wjTCBnJ31bWQ6kiYvbKUbtC44/3jdTskONNXgz8+yGVI8hSjteqzKEdrRkSlA VnFso7+N6Ux3ej8VC5UgUwOv8mxbVxc= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1660894861; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qmEmRwbvgXw29M6tJMACSOhRvv5bpX5gPHGr1QrxjWg=; b=6HSXckWAKOq9QOhFAT2GgBdiJs0SXMFWK+J7rhSeJ7vMKxtcNaIlfGNxUtUDWcI7tJim9e 7iALMLh5xqEszFDg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C6D3D13AC1; Fri, 19 Aug 2022 07:41:01 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id sRHCL40+/2LPUgAAMHmgww (envelope-from ); Fri, 19 Aug 2022 07:41:01 +0000 Date: Fri, 19 Aug 2022 09:41:01 +0200 Message-ID: <87fshs7kaa.wl-tiwai@suse.de> From: Takashi Iwai To: abhishek.shah@columbia.edu Cc: alsa-devel@alsa-project.org, perex@perex.cz, tiwai@suse.com, linux-kernel@vger.kernel.org, Gabriel Ryan Subject: Re: data-race in snd_seq_oss_midi_check_exit_port / snd_seq_oss_midi_setup In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Aug 2022 03:00:00 +0200, Abhishek Shah wrote: > > > Hi all,  > > We found a race involving the max_midi_devs variable. We see an interleaving > where the following check here passes before the > snd_seq_oss_midi_check_exit_port() finishes, but this check should not pass > if max_midi_devs will become zero, but we are not sure of its implications in > terms of security impact. Please let us know what you think. Through a quick glance, I guess it's rather harmless (although a bit fragile from the code sanity POV). A MIDI port could be closed at any time, and the dp->max_mididevs holds locally the upper bound of currently possibly accessible ports. The actual access to each port is done via get_mdev() in seq_oss_midi.c, which is a sort of refcount managed, and it should be fine that a port disappears meanwhile. That said, it'd be even feasible just dropping dp->max_mididevs field and scan all MIDI ports at each time, but it won't bring much benefit, either. thanks, Takashi > > Thanks! > > -------------------Report--------------------- > > write to 0xffffffff88382f80 of 4 bytes by task 6541 on cpu 0: >  snd_seq_oss_midi_check_exit_port+0x1a6/0x270 sound/core/seq/oss/ > seq_oss_midi.c:237 >  receive_announce+0x193/0x1b0 sound/core/seq/oss/seq_oss_init.c:143 >  snd_seq_deliver_single_event+0x30d/0x4e0 sound/core/seq/seq_clientmgr.c:640 >  deliver_to_subscribers sound/core/seq/seq_clientmgr.c:695 [inline] >  snd_seq_deliver_event+0x38c/0x490 sound/core/seq/seq_clientmgr.c:830 >  snd_seq_kernel_client_dispatch+0x189/0x1a0 sound/core/seq/ > seq_clientmgr.c:2339 >  snd_seq_system_broadcast+0x98/0xd0 sound/core/seq/seq_system.c:86 >  snd_seq_ioctl_delete_port+0x9a/0xc0 sound/core/seq/seq_clientmgr.c:1356 >  snd_seq_ioctl+0x198/0x2d0 sound/core/seq/seq_clientmgr.c:2173 >  vfs_ioctl fs/ioctl.c:51 [inline] >  __do_sys_ioctl fs/ioctl.c:870 [inline] >  __se_sys_ioctl+0xe1/0x150 fs/ioctl.c:856 >  __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856 >  do_syscall_x64 arch/x86/entry/common.c:50 [inline] >  do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80 >  entry_SYSCALL_64_after_hwframe+0x44/0xae > > read to 0xffffffff88382f80 of 4 bytes by task 6542 on cpu 1: >  snd_seq_oss_midi_setup+0x1b/0x40 sound/core/seq/oss/seq_oss_midi.c:273 >  snd_seq_oss_open+0x364/0x900 sound/core/seq/oss/seq_oss_init.c:198 >  odev_open+0x55/0x70 sound/core/seq/oss/seq_oss.c:128 >  soundcore_open+0x315/0x3a0 sound/sound_core.c:593 >  chrdev_open+0x373/0x3f0 fs/char_dev.c:414 >  do_dentry_open+0x543/0x8f0 fs/open.c:824 >  vfs_open+0x47/0x50 fs/open.c:958 >  do_open fs/namei.c:3476 [inline] >  path_openat+0x1906/0x1dc0 fs/namei.c:3609 >  do_filp_open+0xef/0x200 fs/namei.c:3636 >  do_sys_openat2+0xa5/0x2a0 fs/open.c:1213 >  do_sys_open fs/open.c:1229 [inline] >  __do_sys_openat fs/open.c:1245 [inline] >  __se_sys_openat fs/open.c:1240 [inline] >  __x64_sys_openat+0xf0/0x120 fs/open.c:1240 >  do_syscall_x64 arch/x86/entry/common.c:50 [inline] >  do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80 >  entry_SYSCALL_64_after_hwframe+0x44/0xae > > Reported by Kernel Concurrency Sanitizer on: > CPU: 1 PID: 6542 Comm: syz-executor2-n Not tainted 5.18.0-rc5+ #107 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/ > 2014 > > Reproducing Inputs > > Input CPU 0: > r0 = openat$sndseq(0xffffffffffffff9c, &(0x7f0000000040)='/dev/snd/seq\x00', > 0x0) > ioctl$SNDRV_SEQ_IOCTL_CREATE_PORT(r0, 0xc0a85320, &(0x7f0000000240)={{0x80}, > 'port1\x00', 0x10}) > ioctl$SNDRV_SEQ_IOCTL_SET_CLIENT_POOL(r0, 0x40a85321, &(0x7f0000000100)= > {0x80}) > > Input CPU 1: > r0 = openat$sequencer2(0xffffff9c, &(0x7f0000000000)='/dev/sequencer2\x00', > 0x0, 0x0) > ioctl$SNDCTL_SYNTH_INFO(r0, 0xc08c5102, &(0x7f0000000200)= > {"02961a3ce6d4828f8b5559726313251b55fa11d8d65406f1f33c9af8e3f8", 0xffffffff}) > >