[PATCH 3.12 031/142] ALSA: dummy: Disable switching timer backend via sysfs

From: Jiri Slaby
Date: Wed Feb 24 2016 - 06:13:23 EST

From: Takashi Iwai <tiwai@xxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 7ee96216c31aabe1eb42fb91ff50dae9fcd014b2 upstream.

ALSA dummy driver can switch the timer backend between system timer
and hrtimer via its hrtimer module option. This can be also switched
dynamically via sysfs, but it may lead to a memory corruption when
switching is done while a PCM stream is running; the stream instance
for the newly switched timer method tries to access the memory that
was allocated by another timer method although the sizes differ.

As the simplest fix, this patch just disables the switch via sysfs by
dropping the writable bit.

BugLink: http://lkml.kernel.org/r/CACT4Y+ZGEeEBntHW5WHn2GoeE0G_kRrCmUh6=dWyy-wfzvuJLg@xxxxxxxxxxxxxx
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
sound/drivers/dummy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
index 915b4d7fbb23..f4d626c05071 100644
--- a/sound/drivers/dummy.c
+++ b/sound/drivers/dummy.c
@@ -87,7 +87,7 @@ MODULE_PARM_DESC(pcm_substreams, "PCM substreams # (1-128) for dummy driver.");
module_param(fake_buffer, bool, 0444);
MODULE_PARM_DESC(fake_buffer, "Fake buffer allocations.");
-module_param(hrtimer, bool, 0644);
+module_param(hrtimer, bool, 0444);
MODULE_PARM_DESC(hrtimer, "Use hrtimer as the timer source.");