[PATCH 3.16 152/204] ALSA: timer: Add missing mutex lock for compat ioctls

From: Ben Hutchings
Date: Thu Dec 28 2017 - 12:27:34 EST


3.16.52-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 79fb0518fec8c8b4ea7f1729f54f293724b3dbb0 upstream.

The races among ioctl and other operations were protected by the
commit af368027a49a ("ALSA: timer: Fix race among timer ioctls") and
later fixes, but one code path was forgotten in the scenario: the
32bit compat ioctl. As syzkaller recently spotted, a very similar
use-after-free may happen with the combination of compat ioctls.

The fix is simply to apply the same ioctl_lock to the compat_ioctl
callback, too.

Fixes: af368027a49a ("ALSA: timer: Fix race among timer ioctls")
Reference: http://lkml.kernel.org/r/089e082686ac9b482e055c832617@xxxxxxxxxx
Reported-by: syzbot <bot+e5f3c9783e7048a74233054febbe9f1bdf54b6da@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
sound/core/timer_compat.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

--- a/sound/core/timer_compat.c
+++ b/sound/core/timer_compat.c
@@ -106,7 +106,8 @@ enum {
#endif /* CONFIG_X86_X32 */
};

-static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg)
+static long __snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd,
+ unsigned long arg)
{
void __user *argp = compat_ptr(arg);

@@ -127,7 +128,7 @@ static long snd_timer_user_ioctl_compat(
case SNDRV_TIMER_IOCTL_PAUSE:
case SNDRV_TIMER_IOCTL_PAUSE_OLD:
case SNDRV_TIMER_IOCTL_NEXT_DEVICE:
- return snd_timer_user_ioctl(file, cmd, (unsigned long)argp);
+ return __snd_timer_user_ioctl(file, cmd, (unsigned long)argp);
case SNDRV_TIMER_IOCTL_INFO32:
return snd_timer_user_info_compat(file, argp);
case SNDRV_TIMER_IOCTL_STATUS32:
@@ -139,3 +140,15 @@ static long snd_timer_user_ioctl_compat(
}
return -ENOIOCTLCMD;
}
+
+static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd,
+ unsigned long arg)
+{
+ struct snd_timer_user *tu = file->private_data;
+ long ret;
+
+ mutex_lock(&tu->ioctl_lock);
+ ret = __snd_timer_user_ioctl_compat(file, cmd, arg);
+ mutex_unlock(&tu->ioctl_lock);
+ return ret;
+}