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ALSA: timer: Add missing mutex lock for compat ioctls

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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@google.com
Reported-by: syzbot <bot+e5f3c9783e7048a74233054febbe9f1bdf54b6da@syzkaller.appspotmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Takashi Iwai 2017-10-29 11:02:04 +01:00 • committed by Greg Kroah-Hartman
parent 27e68f1bca
commit 7035878274
1 changed files with 15 additions and 2 deletions
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17
sound/core/timer_compat.c
View file

@ -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(struct file *file, unsigned int cmd, uns
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(struct file *file, unsigned int cmd, uns
}
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;
}