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[PATCH 3.19.y-ckt 35/47] ALSA: dummy: Disable switching timer backend via sysfs

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3.19.8-ckt15 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Takashi Iwai <tiwai@suse.de>

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@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 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 5d0dfb7..fc041fc 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.");
 #ifdef CONFIG_HIGH_RES_TIMERS
-module_param(hrtimer, bool, 0644);
+module_param(hrtimer, bool, 0444);
 MODULE_PARM_DESC(hrtimer, "Use hrtimer as the timer source.");
 #endif
 
-- 
1.9.1

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[3.19.y-ckt stable] Linux 3.19.8-ckt15 stable review Kamal Mostafa <kamal@canonical.com> - 2016-02-09 23:50 +0100
  [PATCH 3.19.y-ckt 47/47] KEYS: Fix keyring ref leak in join_session_keyring() Kamal Mostafa <kamal@canonical.com> - 2016-02-09 23:50 +0100
  [PATCH 3.19.y-ckt 41/47] perf hists: Fix HISTC_MEM_DCACHELINE width setting Kamal Mostafa <kamal@canonical.com> - 2016-02-09 23:50 +0100
  [PATCH 3.19.y-ckt 11/47] cdc-acm:exclude Samsung phone 04e8:685d Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 10/47] usb: cdc-acm: send zero packet for intel 7260 modem Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 17/47] ALSA: seq: Fix incorrect sanity check at snd_seq_oss_synth_cleanup() Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 35/47] ALSA: dummy: Disable switching timer backend via sysfs Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 34/47] seccomp: always propagate NO_NEW_PRIVS on tsync Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 19/47] USB: serial: ftdi_sio: add support for Yaesu SCU-18 cable Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 23/47] ALSA: usb-audio: Fix TEAC UD-501/UD-503/NT-503 usb delay Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 16/47] USB: serial: option: Adding support for Telit LE922 Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 36/47] drm/vmwgfx: respect 'nomodeset' Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 24/47] ALSA: bebob: Use a signed return type for get_formation_index Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 12/47] usb: hub: do not clear BOS field during reset device Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 09/47] usb: cdc-acm: handle unlinked urb in acm read callback Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 30/47] tty: Fix unsafe ldisc reference via ioctl(TIOCGETD) Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 21/47] USB: option: fix Cinterion AHxx enumeration Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 28/47] powerpc/eeh: Fix PE location code Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 15/47] USB: serial: visor: fix crash on detecting device without write_urbs Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 32/47] staging/speakup: Use tty_ldisc_ref() for paste kworker Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 22/47] ALSA: compress: Disable GET_CODEC_CAPS ioctl for some architectures Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 14/47] USB: visor: fix null-deref at probe Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 26/47] arm64: mm: avoid calling apply_to_page_range on empty range Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 27/47] x86/mm: Fix types used in pgprot cacheability flags translations Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 20/47] arm64: kernel: fix architected PMU registers unconditional access Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 08/47] ACPI / PCI / hotplug: unlock in error path in acpiphp_enable_slot() Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 29/47] SCSI: fix crashes in sd and sr runtime PM Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 25/47] arm64: errata: Add -mpc-relative-literal-loads to build flags Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:00 +0100
  [PATCH 3.19.y-ckt 07/47] ACPI: Revert "ACPI / video: Add Dell Inspiron 5737 to the blacklist" Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:10 +0100
  [PATCH 3.19.y-ckt 03/47] KVM: PPC: Fix emulation of H_SET_DABR/X on POWER8 Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:10 +0100
  [PATCH 3.19.y-ckt 06/47] powerpc: Simplify module TOC handling Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:10 +0100
  [PATCH 3.19.y-ckt 04/47] KVM: PPC: Fix ONE_REG AltiVec support Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:10 +0100
  [PATCH 3.19.y-ckt 02/47] iio: adis_buffer: Fix out-of-bounds memory access Kamal Mostafa <kamal@canonical.com> - 2016-02-10 00:10 +0100

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