BMC/Intel-BMC/linux.git/sound/core/timer.c, branch dev-4.3

ALSA: timer: Fix race between stop and interrupt

2016-02-19T22:28:32+00:00

commit ed8b1d6d2c741ab26d60d499d7fbb7ac801f0f51 upstream. 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 Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Fix wrong instance passed to slave callbacks

2016-02-19T22:28:32+00:00

commit 117159f0b9d392fb433a7871426fad50317f06f7 upstream. 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 Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Fix race at concurrent reads

2016-02-19T22:28:32+00:00

commit 4dff5c7b7093b19c19d3a100f8a3ad87cb7cd9e7 upstream. 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. Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Fix link corruption due to double start or stop

2016-02-19T22:28:32+00:00

commit f784beb75ce82f4136f8a0960d3ee872f7109e09 upstream. 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 Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Fix leftover link at closing

2016-02-19T22:28:31+00:00

commit 094fd3be87b0f102589e2d5c3fa5d06b7e20496d upstream. 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 Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Code cleanup

2016-02-19T22:28:31+00:00

commit c3b1681375dc6e71d89a3ae00cc3ce9e775a8917 upstream. This is a minor code cleanup without any functional changes: - Kill keep_flag argument from _snd_timer_stop(), as all callers pass only it false. - Remove redundant NULL check in _snd_timer_stop(). Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman

ALSA: timer: Handle disconnection more safely

2016-01-31T19:25:48+00:00

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

ALSA: timer: Fix double unlink of active_list

2016-01-31T19:25:47+00:00

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

ALSA: timer: Fix race among timer ioctls

2016-01-31T19:25:47+00:00

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

ALSA: timer: Harden slave timer list handling

2016-01-31T19:25:47+00:00

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