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 [1]consult.awy@gmail.com --- sound/core/control_compat.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c index 470dabc60aa0..edff063e088d 100644 --- a/sound/core/control_compat.c +++ b/sound/core/control_compat.c @@ -264,6 +264,7 @@ 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 || @@ -280,6 +281,8 @@ 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; }

-- 2.25.1

References

1. mailto:consult.awy@gmail.com