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Subject[PATCH 3.16 178/178] ALSA: timer: Fix missing queue indices reset at SNDRV_TIMER_IOCTL_SELECT
3.16.46-rc1 review patch.  If anyone has any objections, please let me know.


From: Takashi Iwai <>

commit ba3021b2c79b2fa9114f92790a99deb27a65b728 upstream.

snd_timer_user_tselect() reallocates the queue buffer dynamically, but
it forgot to reset its indices. Since the read may happen
concurrently with ioctl and snd_timer_user_tselect() allocates the
buffer via kmalloc(), this may lead to the leak of uninitialized
kernel-space data, as spotted via KMSAN:

BUG: KMSAN: use of unitialized memory in snd_timer_user_read+0x6c4/0xa10
CPU: 0 PID: 1037 Comm: probe Not tainted 4.11.0-rc5+ #2739
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16
dump_stack+0x143/0x1b0 lib/dump_stack.c:52
kmsan_report+0x12a/0x180 mm/kmsan/kmsan.c:1007
kmsan_check_memory+0xc2/0x140 mm/kmsan/kmsan.c:1086
copy_to_user ./arch/x86/include/asm/uaccess.h:725
snd_timer_user_read+0x6c4/0xa10 sound/core/timer.c:2004
do_loop_readv_writev fs/read_write.c:716
__do_readv_writev+0x94c/0x1380 fs/read_write.c:864
do_readv_writev fs/read_write.c:894
vfs_readv fs/read_write.c:908
do_readv+0x52a/0x5d0 fs/read_write.c:934
SYSC_readv+0xb6/0xd0 fs/read_write.c:1021
SyS_readv+0x87/0xb0 fs/read_write.c:1018

This patch adds the missing reset of queue indices. Together with the
previous fix for the ioctl/read race, we cover the whole problem.

Reported-by: Alexander Potapenko <>
Tested-by: Alexander Potapenko <>
Signed-off-by: Takashi Iwai <>
Signed-off-by: Ben Hutchings <>
sound/core/timer.c | 1 +
1 file changed, 1 insertion(+)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1636,6 +1636,7 @@ static int snd_timer_user_tselect(struct
if (err < 0)
goto __err;

+ tu->qhead = tu->qtail = tu->qused = 0;
tu->queue = NULL;
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