From: Takashi Iwai Date: Sun, 5 Nov 2017 09:07:43 +0000 (+0100) Subject: ALSA: timer: Limit max instances per timer X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=57a70fe807328d99a7e483592b883b2e8abaca13 ALSA: timer: Limit max instances per timer commit 9b7d869ee5a77ed4a462372bb89af622e705bfb8 upstream. Currently we allow unlimited number of timer instances, and it may bring the system hogging way too much CPU when too many timer instances are opened and processed concurrently. This may end up with a soft-lockup report as triggered by syzkaller, especially when hrtimer backend is deployed. Since such insane number of instances aren't demanded by the normal use case of ALSA sequencer and it merely opens a risk only for abuse, this patch introduces the upper limit for the number of instances per timer backend. As default, it's set to 1000, but for the fine-grained timer like hrtimer, it's set to 100. Reported-by: syzbot Tested-by: Jérôme Glisse Signed-off-by: Takashi Iwai [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- diff --git a/include/sound/timer.h b/include/sound/timer.h index 7990469a44ce..b0489b850c93 100644 --- a/include/sound/timer.h +++ b/include/sound/timer.h @@ -90,6 +90,8 @@ struct snd_timer { struct list_head ack_list_head; struct list_head sack_list_head; /* slow ack list head */ struct tasklet_struct task_queue; + int max_instances; /* upper limit of timer instances */ + int num_instances; /* current number of timer instances */ }; struct snd_timer_instance { diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c index 14d483d6b3b0..834fa602fdd1 100644 --- a/sound/core/hrtimer.c +++ b/sound/core/hrtimer.c @@ -145,6 +145,7 @@ static int __init snd_hrtimer_init(void) timer->hw = hrtimer_hw; timer->hw.resolution = resolution; timer->hw.ticks = NANO_SEC / resolution; + timer->max_instances = 100; /* lower the limit */ err = snd_timer_global_register(timer); if (err < 0) { diff --git a/sound/core/timer.c b/sound/core/timer.c index 80ca9586d9b0..69c801ac025a 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -179,7 +179,7 @@ static void snd_timer_request(struct snd_timer_id *tid) * * call this with register_mutex down. */ -static void snd_timer_check_slave(struct snd_timer_instance *slave) +static int snd_timer_check_slave(struct snd_timer_instance *slave) { struct snd_timer *timer; struct snd_timer_instance *master; @@ -189,16 +189,21 @@ static void snd_timer_check_slave(struct snd_timer_instance *slave) list_for_each_entry(master, &timer->open_list_head, open_list) { if (slave->slave_class == master->slave_class && slave->slave_id == master->slave_id) { + if (master->timer->num_instances >= + master->timer->max_instances) + return -EBUSY; list_move_tail(&slave->open_list, &master->slave_list_head); + master->timer->num_instances++; spin_lock_irq(&slave_active_lock); slave->master = master; slave->timer = master->timer; spin_unlock_irq(&slave_active_lock); - return; + return 0; } } } + return 0; } /* @@ -207,7 +212,7 @@ static void snd_timer_check_slave(struct snd_timer_instance *slave) * * call this with register_mutex down. */ -static void snd_timer_check_master(struct snd_timer_instance *master) +static int snd_timer_check_master(struct snd_timer_instance *master) { struct snd_timer_instance *slave, *tmp; @@ -215,7 +220,11 @@ static void snd_timer_check_master(struct snd_timer_instance *master) list_for_each_entry_safe(slave, tmp, &snd_timer_slave_list, open_list) { if (slave->slave_class == master->slave_class && slave->slave_id == master->slave_id) { + if (master->timer->num_instances >= + master->timer->max_instances) + return -EBUSY; list_move_tail(&slave->open_list, &master->slave_list_head); + master->timer->num_instances++; spin_lock_irq(&slave_active_lock); spin_lock(&master->timer->lock); slave->master = master; @@ -227,8 +236,11 @@ static void snd_timer_check_master(struct snd_timer_instance *master) spin_unlock_irq(&slave_active_lock); } } + return 0; } +static int snd_timer_close_locked(struct snd_timer_instance *timeri); + /* * open a timer instance * when opening a master, the slave id must be here given. @@ -239,6 +251,7 @@ int snd_timer_open(struct snd_timer_instance **ti, { struct snd_timer *timer; struct snd_timer_instance *timeri = NULL; + int err; if (tid->dev_class == SNDRV_TIMER_CLASS_SLAVE) { /* open a slave instance */ @@ -257,10 +270,14 @@ int snd_timer_open(struct snd_timer_instance **ti, timeri->slave_id = tid->device; timeri->flags |= SNDRV_TIMER_IFLG_SLAVE; list_add_tail(&timeri->open_list, &snd_timer_slave_list); - snd_timer_check_slave(timeri); + err = snd_timer_check_slave(timeri); + if (err < 0) { + snd_timer_close_locked(timeri); + timeri = NULL; + } mutex_unlock(®ister_mutex); *ti = timeri; - return 0; + return err; } /* open a master instance */ @@ -286,6 +303,10 @@ int snd_timer_open(struct snd_timer_instance **ti, return -EBUSY; } } + if (timer->num_instances >= timer->max_instances) { + mutex_unlock(®ister_mutex); + return -EBUSY; + } timeri = snd_timer_instance_new(owner, timer); if (!timeri) { mutex_unlock(®ister_mutex); @@ -307,26 +328,28 @@ int snd_timer_open(struct snd_timer_instance **ti, } list_add_tail(&timeri->open_list, &timer->open_list_head); - snd_timer_check_master(timeri); + timer->num_instances++; + err = snd_timer_check_master(timeri); + if (err < 0) { + snd_timer_close_locked(timeri); + timeri = NULL; + } mutex_unlock(®ister_mutex); *ti = timeri; - return 0; + return err; } static int _snd_timer_stop(struct snd_timer_instance *timeri, int event); /* * close a timer instance + * call this with register_mutex down. */ -int snd_timer_close(struct snd_timer_instance *timeri) +static int snd_timer_close_locked(struct snd_timer_instance *timeri) { struct snd_timer *timer = NULL; struct snd_timer_instance *slave, *tmp; - if (snd_BUG_ON(!timeri)) - return -ENXIO; - - mutex_lock(®ister_mutex); list_del(&timeri->open_list); /* force to stop the timer */ @@ -334,6 +357,7 @@ int snd_timer_close(struct snd_timer_instance *timeri) timer = timeri->timer; if (timer) { + timer->num_instances--; /* wait, until the active callback is finished */ spin_lock_irq(&timer->lock); while (timeri->flags & SNDRV_TIMER_IFLG_CALLBACK) { @@ -349,6 +373,7 @@ int snd_timer_close(struct snd_timer_instance *timeri) list_for_each_entry_safe(slave, tmp, &timeri->slave_list_head, open_list) { list_move_tail(&slave->open_list, &snd_timer_slave_list); + timer->num_instances--; slave->master = NULL; slave->timer = NULL; list_del_init(&slave->ack_list); @@ -373,10 +398,25 @@ int snd_timer_close(struct snd_timer_instance *timeri) module_put(timer->module); } - mutex_unlock(®ister_mutex); return 0; } +/* + * close a timer instance + */ +int snd_timer_close(struct snd_timer_instance *timeri) +{ + int err; + + if (snd_BUG_ON(!timeri)) + return -ENXIO; + + mutex_lock(®ister_mutex); + err = snd_timer_close_locked(timeri); + mutex_unlock(®ister_mutex); + return err; +} + unsigned long snd_timer_resolution(struct snd_timer_instance *timeri) { struct snd_timer * timer; @@ -841,6 +881,7 @@ int snd_timer_new(struct snd_card *card, char *id, struct snd_timer_id *tid, spin_lock_init(&timer->lock); tasklet_init(&timer->task_queue, snd_timer_tasklet, (unsigned long)timer); + timer->max_instances = 1000; /* default limit per timer */ if (card != NULL) { timer->module = card->module; err = snd_device_new(card, SNDRV_DEV_TIMER, timer, &ops);