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 F30F2C32774 for ; Tue, 23 Aug 2022 06:56:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240318AbiHWG4w (ORCPT ); Tue, 23 Aug 2022 02:56:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240059AbiHWG4u (ORCPT ); Tue, 23 Aug 2022 02:56:50 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B3105E654 for ; Mon, 22 Aug 2022 23:56:49 -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 042685CE2D; Tue, 23 Aug 2022 06:56:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1661237808; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bqkli4Nux3Wx4xftN5dxoQZEudBfZIfcBHpRPGkS+eE=; b=HVnFhtgbh+OBrVESa1QTLta+HpbHaA4bwNIweMBf2oBjOmhcyvVHGr3x4QRTkwqXohHHy4 WuGj6psBLkdyaDGIlQQWcI2f89A72/4CauVt/IcSNopSPTsRbSI3tdyawd3w9GLG40xmVl wuC072auKGbpL/aJMCxCa83NMM3uTu8= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1661237808; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bqkli4Nux3Wx4xftN5dxoQZEudBfZIfcBHpRPGkS+eE=; b=3j6EZP9YV5g0LQ0ldOo1SYUDI7cz7fSD7LvlyxVVy8YVe86xm3N2lzKYUvZBO9Iae9UW7V 9iDBBYf0kHyxf6Cw== 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 CEBC513A89; Tue, 23 Aug 2022 06:56:47 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id dJiKMS96BGMIMQAAMHmgww (envelope-from ); Tue, 23 Aug 2022 06:56:47 +0000 Date: Tue, 23 Aug 2022 08:56:47 +0200 Message-ID: <87a67vsb0w.wl-tiwai@suse.de> From: Takashi Iwai To: Gabriel Ryan Cc: abhishek.shah@columbia.edu, alsa-devel@alsa-project.org, perex@perex.cz, tiwai@suse.com, linux-kernel@vger.kernel.org Subject: Re: data-race in snd_seq_oss_midi_check_exit_port / snd_seq_oss_midi_setup In-Reply-To: References: <87fshs7kaa.wl-tiwai@suse.de> 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=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Aug 2022 22:00:42 +0200, Gabriel Ryan wrote: > > Hi Takashi, > > Makes sense, we'll note this race as benign for our future reference. > > Thanks for taking the time to look at this! Although it's more or less harmless, the data-race should be still addressed. I'm going to submit the fixes for both issues you've reported. thanks, Takashi > > Best, > > Gabe > > On Fri, Aug 19, 2022 at 3:41 AM Takashi Iwai wrote: > > > > 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}) > > > > > > > > -- > Gabriel Ryan > PhD Candidate at Columbia University >