From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AC31130CD92 for ; Sat, 25 Jul 2026 06:53:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.130 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784962436; cv=none; b=PcVZFdhF4MzwJrRpg57jhY1p/FIyS37jb3i3apJ4GUweG73uZaIQJTO4qvn0a3Ou+MHQeMLeDSXezbtQl9zjgM7CTO6xG/HeM6HP6jxpzDdAu2g0YRrbKda8hRu8rlDYZdiYUZ8k+fjteUM+zOg0o7Fd85S1hnn3sPd/w3setsI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784962436; c=relaxed/simple; bh=bhkwJoYNQ5LPlLklCMjnc2s/W8QsleX0Eub7qWrm8hE=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=ebTZkuEKx4PiMS0qSdL2jrg6K7sUjECufETUGGXAUi87mReE8q7e8DSPU/U3I/KF8s9T1nnS3Brfu8Ij7U/0136kgVlcnxkRPmxjw9IAaYTib8V4PCOcSTyL0cv5zlBYBObptzsN03qZJWAJyLzg/OOI9BMzTQ1R2bx/r9/E+f8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de; spf=pass smtp.mailfrom=suse.de; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=rs6b8o2R; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=/n+0zg0R; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b=rs6b8o2R; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b=/n+0zg0R; arc=none smtp.client-ip=195.135.223.130 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="rs6b8o2R"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="/n+0zg0R"; dkim=pass (1024-bit key) header.d=suse.de header.i=@suse.de header.b="rs6b8o2R"; dkim=permerror (0-bit key) header.d=suse.de header.i=@suse.de header.b="/n+0zg0R" Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (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 smtp-out1.suse.de (Postfix) with ESMTPS id 827E77C13B; Sat, 25 Jul 2026 06:53:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1784962432; 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=aV4QhpimtuHzG5VoHM46VGYUqHQ/va9Qf28pdQbxoaA=; b=rs6b8o2RVRAG2d82CTlzksRGh9nAsOvxrpg3BPnQ5dGjWqxdarFv7SBoFA+AZyUxIpS8P2 1Laud8Cb59tdBz3wr0hewKkMc03wuPyYJL46kajVD5qULlx9pdCcVMs9uygyJXldaYBZbH MZiNwC0Jocyhexse77MvkhkpevvvSys= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1784962432; 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=aV4QhpimtuHzG5VoHM46VGYUqHQ/va9Qf28pdQbxoaA=; b=/n+0zg0RLhZkCkOiPaSQ+Cso6DZBEZnl7ZGAIl6iAVi7IqmVwQW76hRrQCkbIF4SqighJb yZjeq23Lktqh8aDA== Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=rs6b8o2R; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b="/n+0zg0R" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1784962432; 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=aV4QhpimtuHzG5VoHM46VGYUqHQ/va9Qf28pdQbxoaA=; b=rs6b8o2RVRAG2d82CTlzksRGh9nAsOvxrpg3BPnQ5dGjWqxdarFv7SBoFA+AZyUxIpS8P2 1Laud8Cb59tdBz3wr0hewKkMc03wuPyYJL46kajVD5qULlx9pdCcVMs9uygyJXldaYBZbH MZiNwC0Jocyhexse77MvkhkpevvvSys= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1784962432; 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=aV4QhpimtuHzG5VoHM46VGYUqHQ/va9Qf28pdQbxoaA=; b=/n+0zg0RLhZkCkOiPaSQ+Cso6DZBEZnl7ZGAIl6iAVi7IqmVwQW76hRrQCkbIF4SqighJb yZjeq23Lktqh8aDA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (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 imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 5E8C9779B9; Sat, 25 Jul 2026 06:53:52 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id moahFYBdZGqHZAAAD6G6ig (envelope-from ); Sat, 25 Jul 2026 06:53:52 +0000 Date: Sat, 25 Jul 2026 08:53:52 +0200 Message-ID: <87tspnblvj.wl-tiwai@suse.de> From: Takashi Iwai To: Norbert Szetei Cc: linux-sound@vger.kernel.org, Takashi Iwai , Jaroslav Kysela Subject: Re: [PATCH] ALSA: seq: Fix division by zero in initialize_timer() In-Reply-To: References: User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Score: -3.51 X-Spam-Level: X-Rspamd-Action: no action X-Rspamd-Queue-Id: 827E77C13B X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO On Sat, 25 Jul 2026 08:33:45 +0200, Norbert Szetei wrote: > > A userspace-driven ALSA timer (SND_UTIMER) lets an unprivileged user set > the backing snd_timer's hardware resolution to an arbitrary 64-bit value > via SNDRV_TIMER_IOCTL_CREATE. snd_utimer_create() only rejects zero. > > When such a timer is bound to a sequencer queue, initialize_timer() > computes the tick period as > > tmr->ticks = 1000000000 / (r * freq); > > where r is that user-controlled resolution and freq is the sequencer > update rate in Hz, clamped to MIN_FREQUENCY..MAX_FREQUENCY (10..6250). > A resolution of 2^63 makes the 64-bit product r * freq wrap to zero for > any even freq, including DEFAULT_FREQUENCY (1000), so the division faults > with a divide-by-zero. > > The division runs under tmr->lock with interrupts disabled, so the oops > leaves the spinlock held and hangs the CPU. It is reachable by an > unprivileged user with access to /dev/snd/timer and /dev/snd/seq. > > Oops: divide error: 0000 [#1] SMP KASAN PTI > CPU: 7 UID: 1000 PID: 456 Comm: alsa_seq_utimer Not tainted 7.2.0-rc4+ > RIP: 0010:initialize_timer.constprop.0+0x20a/0x2d0 > snd_seq_timer_start+0x15e/0x2b0 > snd_seq_control_queue+0x56f/0xba0 > snd_seq_write+0x3e0/0x730 > > Reject an overflowing product with check_mul_overflow() and fall back to > a single tick, which also avoids feeding a wrapped-but-nonzero divisor > (e.g. 2^63 * 1000 mod 2^64 == 0, or other resolutions wrapping to a small > value) into the period computation. > > Fixes: 37745918e0e7 ("ALSA: timer: Introduce virtual userspace-driven timers") > Cc: > Assisted-by: Claude:claude-opus-4-8 > Signed-off-by: Norbert Szetei Thanks, applied now. Takashi