From: Alan Young <consult.awy@xxxxxxxxx> 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: Alan Young <consult.awy@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20211202150607.543389-1-consult.awy@xxxxxxxxx Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- sound/core/control_compat.c | 3 +++ 1 file changed, 3 insertions(+) --- a/sound/core/control_compat.c +++ b/sound/core/control_compat.c @@ -264,6 +264,7 @@ static int copy_ctl_value_to_user(void _ 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 || @@ -280,6 +281,8 @@ static int copy_ctl_value_to_user(void _ 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; }
