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    Subject[PATCH 4.19 24/74] ALSA: ctl: Fix copy of updated id with element read/write
    Date
    From: Alan Young <consult.awy@gmail.com>

    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@gmail.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/20211202150607.543389-1-consult.awy@gmail.com
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    sound/core/control_compat.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/sound/core/control_compat.c
    +++ b/sound/core/control_compat.c
    @@ -279,6 +279,7 @@ 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 ||
    @@ -295,6 +296,8 @@ 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;
    }


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