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Commit fd753901 authored by Alan Young's avatar Alan Young Committed by Greg Kroah-Hartman
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ALSA: ctl: Fix copy of updated id with element read/write 



commit b6409dd6bdc03aa178bbff0d80db2a30d29b63ac upstream.

When control_compat.c:copy_ctl_value_to_user() is used, by
ctl_elem_read_user() & ctl_elem_write_user(), it must also copy back the
snd_ctl_elem_id value that may have been updated (filled in) by the call
to snd_ctl_elem_read/snd_ctl_elem_write().

This matches the functionality provided by snd_ctl_elem_read_user() and
snd_ctl_elem_write_user(), via snd_ctl_build_ioff().

Without this, and without making additional calls to snd_ctl_info()
which are unnecessary when using the non-compat calls, a userspace
application will not know the numid value for the element and
consequently will not be able to use the poll/read interface on the
control file to determine which elements have updates.

Signed-off-by: default avatarAlan Young <consult.awy@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211202150607.543389-1-consult.awy@gmail.com


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 505039dd

sound/core/control_compat.c

+3 −0
Original line number Diff line number Diff line
@@ -279,6 +279,7 @@ static int copy_ctl_value_to_user(void __user *userdata, 
				  struct snd_ctl_elem_value *data,

				  int type, int count)

{

	struct snd_ctl_elem_value32 __user *data32 = userdata;

	int i, size;



	if (type == SNDRV_CTL_ELEM_TYPE_BOOLEAN ||
@@ -295,6 +296,8 @@ static int copy_ctl_value_to_user(void __user *userdata, 
		if (copy_to_user(valuep, data->value.bytes.data, size))

			return -EFAULT;

	}

	if (copy_to_user(&data32->id, &data->id, sizeof(data32->id)))

		return -EFAULT;

	return 0;

}