From ea7f3d59628930dc29482a292e2a55c81cac52a4 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 14 Jan 2016 16:30:58 +0100 Subject: ALSA: timer: Harden slave timer list handling commit b5a663aa426f4884c71cd8580adae73f33570f0d upstream. A slave timer instance might be still accessible in a racy way while operating the master instance as it lacks of locking. Since the master operation is mostly protected with timer->lock, we should cope with it while changing the slave instance, too. Also, some linked lists (active_list and ack_list) of slave instances aren't unlinked immediately at stopping or closing, and this may lead to unexpected accesses. This patch tries to address these issues. It adds spin lock of timer->lock (either from master or slave, which is equivalent) in a few places. For avoiding a deadlock, we ensure that the global slave_active_lock is always locked at first before each timer lock. Also, ack and active_list of slave instances are properly unlinked at snd_timer_stop() and snd_timer_close(). Last but not least, remove the superfluous call of _snd_timer_stop() at removing slave links. This is a noop, and calling it may confuse readers wrt locking. Further cleanup will follow in a later patch. Actually we've got reports of use-after-free by syzkaller fuzzer, and this hopefully fixes these issues. Reported-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/timer.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index 31f40f03e5b7..8b06413e967e 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -215,11 +215,13 @@ static void snd_timer_check_master(struct snd_timer_instance *master) slave->slave_id == master->slave_id) { list_move_tail(&slave->open_list, &master->slave_list_head); spin_lock_irq(&slave_active_lock); + spin_lock(&master->timer->lock); slave->master = master; slave->timer = master->timer; if (slave->flags & SNDRV_TIMER_IFLG_RUNNING) list_add_tail(&slave->active_list, &master->slave_active_head); + spin_unlock(&master->timer->lock); spin_unlock_irq(&slave_active_lock); } } @@ -346,15 +348,18 @@ int snd_timer_close(struct snd_timer_instance *timeri) timer->hw.close) timer->hw.close(timer); /* remove slave links */ + spin_lock_irq(&slave_active_lock); + spin_lock(&timer->lock); list_for_each_entry_safe(slave, tmp, &timeri->slave_list_head, open_list) { - spin_lock_irq(&slave_active_lock); - _snd_timer_stop(slave, 1, SNDRV_TIMER_EVENT_RESOLUTION); list_move_tail(&slave->open_list, &snd_timer_slave_list); slave->master = NULL; slave->timer = NULL; - spin_unlock_irq(&slave_active_lock); + list_del_init(&slave->ack_list); + list_del_init(&slave->active_list); } + spin_unlock(&timer->lock); + spin_unlock_irq(&slave_active_lock); mutex_unlock(®ister_mutex); } out: @@ -441,9 +446,12 @@ static int snd_timer_start_slave(struct snd_timer_instance *timeri) spin_lock_irqsave(&slave_active_lock, flags); timeri->flags |= SNDRV_TIMER_IFLG_RUNNING; - if (timeri->master) + if (timeri->master && timeri->timer) { + spin_lock(&timeri->timer->lock); list_add_tail(&timeri->active_list, &timeri->master->slave_active_head); + spin_unlock(&timeri->timer->lock); + } spin_unlock_irqrestore(&slave_active_lock, flags); return 1; /* delayed start */ } @@ -489,6 +497,8 @@ static int _snd_timer_stop(struct snd_timer_instance * timeri, if (!keep_flag) { spin_lock_irqsave(&slave_active_lock, flags); timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; + list_del_init(&timeri->ack_list); + list_del_init(&timeri->active_list); spin_unlock_irqrestore(&slave_active_lock, flags); } goto __end; -- cgit v1.2.3 From 7066da22b1eb40e955f9dfe57022816fae53d3cf Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 13 Jan 2016 17:48:01 +0100 Subject: ALSA: timer: Fix race among timer ioctls commit af368027a49a751d6ff4ee9e3f9961f35bb4fede upstream. ALSA timer ioctls have an open race and this may lead to a use-after-free of timer instance object. A simplistic fix is to make each ioctl exclusive. We have already tread_sem for controlling the tread, and extend this as a global mutex to be applied to each ioctl. The downside is, of course, the worse concurrency. But these ioctls aren't to be parallel accessible, in anyway, so it should be fine to serialize there. Reported-by: Dmitry Vyukov Tested-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/timer.c | 32 +++++++++++++++++++------------- 1 file changed, 19 insertions(+), 13 deletions(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index 8b06413e967e..b0458285723a 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -73,7 +73,7 @@ struct snd_timer_user { struct timespec tstamp; /* trigger tstamp */ wait_queue_head_t qchange_sleep; struct fasync_struct *fasync; - struct mutex tread_sem; + struct mutex ioctl_lock; }; /* list of timers */ @@ -1263,7 +1263,7 @@ static int snd_timer_user_open(struct inode *inode, struct file *file) return -ENOMEM; spin_lock_init(&tu->qlock); init_waitqueue_head(&tu->qchange_sleep); - mutex_init(&tu->tread_sem); + mutex_init(&tu->ioctl_lock); tu->ticks = 1; tu->queue_size = 128; tu->queue = kmalloc(tu->queue_size * sizeof(struct snd_timer_read), @@ -1283,8 +1283,10 @@ static int snd_timer_user_release(struct inode *inode, struct file *file) if (file->private_data) { tu = file->private_data; file->private_data = NULL; + mutex_lock(&tu->ioctl_lock); if (tu->timeri) snd_timer_close(tu->timeri); + mutex_unlock(&tu->ioctl_lock); kfree(tu->queue); kfree(tu->tqueue); kfree(tu); @@ -1522,7 +1524,6 @@ static int snd_timer_user_tselect(struct file *file, int err = 0; tu = file->private_data; - mutex_lock(&tu->tread_sem); if (tu->timeri) { snd_timer_close(tu->timeri); tu->timeri = NULL; @@ -1566,7 +1567,6 @@ static int snd_timer_user_tselect(struct file *file, } __err: - mutex_unlock(&tu->tread_sem); return err; } @@ -1779,7 +1779,7 @@ enum { SNDRV_TIMER_IOCTL_PAUSE_OLD = _IO('T', 0x23), }; -static long snd_timer_user_ioctl(struct file *file, unsigned int cmd, +static long __snd_timer_user_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct snd_timer_user *tu; @@ -1796,17 +1796,11 @@ static long snd_timer_user_ioctl(struct file *file, unsigned int cmd, { int xarg; - mutex_lock(&tu->tread_sem); - if (tu->timeri) { /* too late */ - mutex_unlock(&tu->tread_sem); + if (tu->timeri) /* too late */ return -EBUSY; - } - if (get_user(xarg, p)) { - mutex_unlock(&tu->tread_sem); + if (get_user(xarg, p)) return -EFAULT; - } tu->tread = xarg ? 1 : 0; - mutex_unlock(&tu->tread_sem); return 0; } case SNDRV_TIMER_IOCTL_GINFO: @@ -1839,6 +1833,18 @@ static long snd_timer_user_ioctl(struct file *file, unsigned int cmd, return -ENOTTY; } +static long snd_timer_user_ioctl(struct file *file, unsigned int cmd, + unsigned long arg) +{ + struct snd_timer_user *tu = file->private_data; + long ret; + + mutex_lock(&tu->ioctl_lock); + ret = __snd_timer_user_ioctl(file, cmd, arg); + mutex_unlock(&tu->ioctl_lock); + return ret; +} + static int snd_timer_user_fasync(int fd, struct file * file, int on) { struct snd_timer_user *tu; -- cgit v1.2.3 From baa3a675b24fe17d5e514d71561d97f46bc6086f Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 13 Jan 2016 21:35:06 +0100 Subject: ALSA: timer: Fix double unlink of active_list commit ee8413b01045c74340aa13ad5bdf905de32be736 upstream. ALSA timer instance object has a couple of linked lists and they are unlinked unconditionally at snd_timer_stop(). Meanwhile snd_timer_interrupt() unlinks it, but it calls list_del() which leaves the element list itself unchanged. This ends up with unlinking twice, and it was caught by syzkaller fuzzer. The fix is to use list_del_init() variant properly there, too. Reported-by: Dmitry Vyukov Tested-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/timer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index b0458285723a..4e8d7bfffff6 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -704,7 +704,7 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left) } else { ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING; if (--timer->running) - list_del(&ti->active_list); + list_del_init(&ti->active_list); } if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) || (ti->flags & SNDRV_TIMER_IFLG_FAST)) -- cgit v1.2.3 From 06b00accf521abfdce83cf8d34069445a35799d2 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 21 Jan 2016 17:19:31 +0100 Subject: ALSA: timer: Handle disconnection more safely commit 230323dac060123c340cf75997971145a42661ee upstream. Currently ALSA timer device doesn't take the disconnection into account very well; it merely unlinks the timer device at disconnection callback but does nothing else. Because of this, when an application accessing the timer device is disconnected, it may release the resource before actually closed. In most cases, it results in a warning message indicating a leftover timer instance like: ALSA: timer xxxx is busy? But basically this is an open race. This patch tries to address it. The strategy is like other ALSA devices: namely, - Manage card's refcount at each open/close - Wake up the pending tasks at disconnection - Check the shutdown flag appropriately at each possible call Note that this patch has one ugly hack to handle the wakeup of pending tasks. It'd be cleaner to introduce a new disconnect op to snd_timer_instance ops. But since it would lead to internal ABI breakage and it eventually increase my own work when backporting to stable kernels, I took a different path to implement locally in timer.c. A cleanup patch will follow at next for 4.5 kernel. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=109431 Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/timer.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index 4e8d7bfffff6..0a049c4578f1 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -65,6 +65,7 @@ struct snd_timer_user { int qtail; int qused; int queue_size; + bool disconnected; struct snd_timer_read *queue; struct snd_timer_tread *tqueue; spinlock_t qlock; @@ -290,6 +291,9 @@ int snd_timer_open(struct snd_timer_instance **ti, mutex_unlock(®ister_mutex); return -ENOMEM; } + /* take a card refcount for safe disconnection */ + if (timer->card) + get_device(&timer->card->card_dev); timeri->slave_class = tid->dev_sclass; timeri->slave_id = slave_id; if (list_empty(&timer->open_list_head) && timer->hw.open) @@ -360,6 +364,9 @@ int snd_timer_close(struct snd_timer_instance *timeri) } spin_unlock(&timer->lock); spin_unlock_irq(&slave_active_lock); + /* release a card refcount for safe disconnection */ + if (timer->card) + put_device(&timer->card->card_dev); mutex_unlock(®ister_mutex); } out: @@ -475,6 +482,8 @@ int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks) timer = timeri->timer; if (timer == NULL) return -EINVAL; + if (timer->card && timer->card->shutdown) + return -ENODEV; spin_lock_irqsave(&timer->lock, flags); timeri->ticks = timeri->cticks = ticks; timeri->pticks = 0; @@ -509,6 +518,10 @@ static int _snd_timer_stop(struct snd_timer_instance * timeri, spin_lock_irqsave(&timer->lock, flags); list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); + if (timer->card && timer->card->shutdown) { + spin_unlock_irqrestore(&timer->lock, flags); + return 0; + } if ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) && !(--timer->running)) { timer->hw.stop(timer); @@ -571,6 +584,8 @@ int snd_timer_continue(struct snd_timer_instance *timeri) timer = timeri->timer; if (! timer) return -EINVAL; + if (timer->card && timer->card->shutdown) + return -ENODEV; spin_lock_irqsave(&timer->lock, flags); if (!timeri->cticks) timeri->cticks = 1; @@ -634,6 +649,9 @@ static void snd_timer_tasklet(unsigned long arg) unsigned long resolution, ticks; unsigned long flags; + if (timer->card && timer->card->shutdown) + return; + spin_lock_irqsave(&timer->lock, flags); /* now process all callbacks */ while (!list_empty(&timer->sack_list_head)) { @@ -674,6 +692,9 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left) if (timer == NULL) return; + if (timer->card && timer->card->shutdown) + return; + spin_lock_irqsave(&timer->lock, flags); /* remember the current resolution */ @@ -884,11 +905,28 @@ static int snd_timer_dev_register(struct snd_device *dev) return 0; } +/* just for reference in snd_timer_dev_disconnect() below */ +static void snd_timer_user_ccallback(struct snd_timer_instance *timeri, + int event, struct timespec *tstamp, + unsigned long resolution); + static int snd_timer_dev_disconnect(struct snd_device *device) { struct snd_timer *timer = device->device_data; + struct snd_timer_instance *ti; + mutex_lock(®ister_mutex); list_del_init(&timer->device_list); + /* wake up pending sleepers */ + list_for_each_entry(ti, &timer->open_list_head, open_list) { + /* FIXME: better to have a ti.disconnect() op */ + if (ti->ccallback == snd_timer_user_ccallback) { + struct snd_timer_user *tu = ti->callback_data; + + tu->disconnected = true; + wake_up(&tu->qchange_sleep); + } + } mutex_unlock(®ister_mutex); return 0; } @@ -899,6 +937,8 @@ void snd_timer_notify(struct snd_timer *timer, int event, struct timespec *tstam unsigned long resolution = 0; struct snd_timer_instance *ti, *ts; + if (timer->card && timer->card->shutdown) + return; if (! (timer->hw.flags & SNDRV_TIMER_HW_SLAVE)) return; if (snd_BUG_ON(event < SNDRV_TIMER_EVENT_MSTART || @@ -1057,6 +1097,8 @@ static void snd_timer_proc_read(struct snd_info_entry *entry, mutex_lock(®ister_mutex); list_for_each_entry(timer, &snd_timer_list, device_list) { + if (timer->card && timer->card->shutdown) + continue; switch (timer->tmr_class) { case SNDRV_TIMER_CLASS_GLOBAL: snd_iprintf(buffer, "G%i: ", timer->tmr_device); @@ -1882,6 +1924,10 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, remove_wait_queue(&tu->qchange_sleep, &wait); + if (tu->disconnected) { + err = -ENODEV; + break; + } if (signal_pending(current)) { err = -ERESTARTSYS; break; @@ -1931,6 +1977,8 @@ static unsigned int snd_timer_user_poll(struct file *file, poll_table * wait) mask = 0; if (tu->qused) mask |= POLLIN | POLLRDNORM; + if (tu->disconnected) + mask |= POLLERR; return mask; } -- cgit v1.2.3