From f784beb75ce82f4136f8a0960d3ee872f7109e09 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Sat, 30 Jan 2016 23:09:08 +0100 Subject: ALSA: timer: Fix link corruption due to double start or stop Although ALSA timer code got hardening for races, it still causes use-after-free error. This is however rather a corrupted linked list, not actually the concurrent accesses. Namely, when timer start is triggered twice, list_add_tail() is called twice, too. This ends up with the link corruption and triggers KASAN error. The simplest fix would be replacing list_add_tail() with list_move_tail(), but fundamentally it's the problem that we don't check the double start/stop correctly. So, the right fix here is to add the proper checks to snd_timer_start() and snd_timer_stop() (and their variants). BugLink: http://lkml.kernel.org/r/CACT4Y+ZyPRoMQjmawbvmCEDrkBD2BQuH7R09=eOkf5ESK8kJAw@mail.gmail.com Reported-by: Dmitry Vyukov Cc: Signed-off-by: Takashi Iwai --- sound/core/timer.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index af1f68f7e315..12db60dd147b 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -451,6 +451,10 @@ static int snd_timer_start_slave(struct snd_timer_instance *timeri) unsigned long flags; spin_lock_irqsave(&slave_active_lock, flags); + if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) { + spin_unlock_irqrestore(&slave_active_lock, flags); + return -EBUSY; + } timeri->flags |= SNDRV_TIMER_IFLG_RUNNING; if (timeri->master && timeri->timer) { spin_lock(&timeri->timer->lock); @@ -475,7 +479,8 @@ int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks) return -EINVAL; if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { result = snd_timer_start_slave(timeri); - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); + if (result >= 0) + snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); return result; } timer = timeri->timer; @@ -484,11 +489,18 @@ int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks) if (timer->card && timer->card->shutdown) return -ENODEV; spin_lock_irqsave(&timer->lock, flags); + if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | + SNDRV_TIMER_IFLG_START)) { + result = -EBUSY; + goto unlock; + } timeri->ticks = timeri->cticks = ticks; timeri->pticks = 0; result = snd_timer_start1(timer, timeri, ticks); + unlock: spin_unlock_irqrestore(&timer->lock, flags); - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); + if (result >= 0) + snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); return result; } @@ -502,6 +514,10 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { spin_lock_irqsave(&slave_active_lock, flags); + if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) { + spin_unlock_irqrestore(&slave_active_lock, flags); + return -EBUSY; + } timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); @@ -512,6 +528,11 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) if (!timer) return -EINVAL; spin_lock_irqsave(&timer->lock, flags); + if (!(timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | + SNDRV_TIMER_IFLG_START))) { + spin_unlock_irqrestore(&timer->lock, flags); + return -EBUSY; + } list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); if (timer->card && timer->card->shutdown) { @@ -581,10 +602,15 @@ int snd_timer_continue(struct snd_timer_instance *timeri) if (timer->card && timer->card->shutdown) return -ENODEV; spin_lock_irqsave(&timer->lock, flags); + if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) { + result = -EBUSY; + goto unlock; + } if (!timeri->cticks) timeri->cticks = 1; timeri->pticks = 0; result = snd_timer_start1(timer, timeri, timer->sticks); + unlock: spin_unlock_irqrestore(&timer->lock, flags); snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_CONTINUE); return result; -- cgit v1.2.3 From f146357f069e71aff8e474c625bcebcd3094b3ab Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 2 Feb 2016 14:14:10 +0100 Subject: ALSA: timer: Sync timer deletion at closing the system timer ALSA timer core framework has no sync point at stopping because it's called inside the spinlock. Thus we need a sync point at close for avoiding the stray timer task. This is simply done by implementing the close callback just calling del_timer_sync(). (It's harmless to call it unconditionally, as the core timer itself cares of the already deleted timer instance.) Signed-off-by: Takashi Iwai --- sound/core/timer.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index 12db60dd147b..b419e612f987 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1058,11 +1058,21 @@ static int snd_timer_s_stop(struct snd_timer * timer) return 0; } +static int snd_timer_s_close(struct snd_timer *timer) +{ + struct snd_timer_system_private *priv; + + priv = (struct snd_timer_system_private *)timer->private_data; + del_timer_sync(&priv->tlist); + return 0; +} + static struct snd_timer_hardware snd_timer_system = { .flags = SNDRV_TIMER_HW_FIRST | SNDRV_TIMER_HW_TASKLET, .resolution = 1000000000L / HZ, .ticks = 10000000L, + .close = snd_timer_s_close, .start = snd_timer_s_start, .stop = snd_timer_s_stop }; -- cgit v1.2.3 From 094fd3be87b0f102589e2d5c3fa5d06b7e20496d Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 4 Feb 2016 17:06:13 +0100 Subject: ALSA: timer: Fix leftover link at closing In ALSA timer core, the active timer instance is managed in active_list linked list. Each element is added / removed dynamically at timer start, stop and in timer interrupt. The problem is that snd_timer_interrupt() has a thinko and leaves the element in active_list when it's the last opened element. This eventually leads to list corruption or use-after-free error. This hasn't been revealed because we used to delete the list forcibly in snd_timer_stop() in the past. However, the recent fix avoids the double-stop behavior (in commit [f784beb75ce8: ALSA: timer: Fix link corruption due to double start or stop]), and this leak hits reality. This patch fixes the link management in snd_timer_interrupt(). Now it simply unlinks no matter which stream is. BugLink: http://lkml.kernel.org/r/CACT4Y+Yy2aukHP-EDp8-ziNqNNmb-NTf=jDWXMP7jB8HDa2vng@mail.gmail.com Reported-by: Dmitry Vyukov Cc: Signed-off-by: Takashi Iwai --- sound/core/timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index b419e612f987..9b513a05765a 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -744,8 +744,8 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left) ti->cticks = ti->ticks; } else { ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING; - if (--timer->running) - list_del_init(&ti->active_list); + --timer->running; + 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 117159f0b9d392fb433a7871426fad50317f06f7 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Mon, 8 Feb 2016 17:36:25 +0100 Subject: ALSA: timer: Fix wrong instance passed to slave callbacks In snd_timer_notify1(), the wrong timer instance was passed for slave ccallback function. This leads to the access to the wrong data when an incompatible master is handled (e.g. the master is the sequencer timer and the slave is a user timer), as spotted by syzkaller fuzzer. This patch fixes that wrong assignment. BugLink: http://lkml.kernel.org/r/CACT4Y+Y_Bm+7epAb=8Wi=AaWd+DYS7qawX52qxdCfOfY49vozQ@mail.gmail.com Reported-by: Dmitry Vyukov Cc: Signed-off-by: Takashi Iwai --- 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 9b513a05765a..dea932ac6165 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -422,7 +422,7 @@ static void snd_timer_notify1(struct snd_timer_instance *ti, int event) spin_lock_irqsave(&timer->lock, flags); list_for_each_entry(ts, &ti->slave_active_head, active_list) if (ts->ccallback) - ts->ccallback(ti, event + 100, &tstamp, resolution); + ts->ccallback(ts, event + 100, &tstamp, resolution); spin_unlock_irqrestore(&timer->lock, flags); } -- cgit v1.2.3 From ed8b1d6d2c741ab26d60d499d7fbb7ac801f0f51 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Tue, 9 Feb 2016 12:02:32 +0100 Subject: ALSA: timer: Fix race between stop and interrupt A slave timer element also unlinks at snd_timer_stop() but it takes only slave_active_lock. When a slave is assigned to a master, however, this may become a race against the master's interrupt handling, eventually resulting in a list corruption. The actual bug could be seen with a syzkaller fuzzer test case in BugLink below. As a fix, we need to take timeri->timer->lock when timer isn't NULL, i.e. assigned to a master, while the assignment to a master itself is protected by slave_active_lock. BugLink: http://lkml.kernel.org/r/CACT4Y+Y_Bm+7epAb=8Wi=AaWd+DYS7qawX52qxdCfOfY49vozQ@mail.gmail.com Cc: Signed-off-by: Takashi Iwai --- sound/core/timer.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index dea932ac6165..a0405b0078c6 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -518,9 +518,13 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event) spin_unlock_irqrestore(&slave_active_lock, flags); return -EBUSY; } + if (timeri->timer) + spin_lock(&timeri->timer->lock); timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); + if (timeri->timer) + spin_unlock(&timeri->timer->lock); spin_unlock_irqrestore(&slave_active_lock, flags); goto __end; } -- cgit v1.2.3 From 4dff5c7b7093b19c19d3a100f8a3ad87cb7cd9e7 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Mon, 8 Feb 2016 17:26:58 +0100 Subject: ALSA: timer: Fix race at concurrent reads snd_timer_user_read() has a potential race among parallel reads, as qhead and qused are updated outside the critical section due to copy_to_user() calls. Move them into the critical section, and also sanitize the relevant code a bit. Cc: Signed-off-by: Takashi Iwai --- sound/core/timer.c | 34 +++++++++++++++------------------- 1 file changed, 15 insertions(+), 19 deletions(-) (limited to 'sound/core/timer.c') diff --git a/sound/core/timer.c b/sound/core/timer.c index a0405b0078c6..dca817fc7894 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1933,6 +1933,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, { struct snd_timer_user *tu; long result = 0, unit; + int qhead; int err = 0; tu = file->private_data; @@ -1944,7 +1945,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) { err = -EAGAIN; - break; + goto _error; } set_current_state(TASK_INTERRUPTIBLE); @@ -1959,42 +1960,37 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, if (tu->disconnected) { err = -ENODEV; - break; + goto _error; } if (signal_pending(current)) { err = -ERESTARTSYS; - break; + goto _error; } } + qhead = tu->qhead++; + tu->qhead %= tu->queue_size; spin_unlock_irq(&tu->qlock); - if (err < 0) - goto _error; if (tu->tread) { - if (copy_to_user(buffer, &tu->tqueue[tu->qhead++], - sizeof(struct snd_timer_tread))) { + if (copy_to_user(buffer, &tu->tqueue[qhead], + sizeof(struct snd_timer_tread))) err = -EFAULT; - goto _error; - } } else { - if (copy_to_user(buffer, &tu->queue[tu->qhead++], - sizeof(struct snd_timer_read))) { + if (copy_to_user(buffer, &tu->queue[qhead], + sizeof(struct snd_timer_read))) err = -EFAULT; - goto _error; - } } - tu->qhead %= tu->queue_size; - - result += unit; - buffer += unit; - spin_lock_irq(&tu->qlock); tu->qused--; + if (err < 0) + goto _error; + result += unit; + buffer += unit; } - spin_unlock_irq(&tu->qlock); _error: + spin_unlock_irq(&tu->qlock); return result > 0 ? result : err; } -- cgit v1.2.3