[PATCH] Fix an OOB bug in uac_mixer_unit_bmControls

[Hui Peng]

`uac_mixer_unit_get_channels` calls `uac_mixer_unit_bmControls`
to get pointer to bmControls field. The current implementation of
`uac_mixer_unit_get_channels` does properly check the size of
uac_mixer_unit_descriptor descriptor and may allow OOB access
in `uac_mixer_unit_bmControls`.

Reported-by: Hui Peng <benqu...@gmail.com>
Reported-by: Mathias Payer <mathias.pa...@nebelwelt.net>
Signed-off-by: Hui Peng <benqu...@gmail.com>
---
 sound/usb/mixer.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index b5927c3d5bc0..00e6274a63c3 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -738,28 +738,39 @@ static int get_cluster_channels_v3(struct mixer_build 
*state, unsigned int clust
 static int uac_mixer_unit_get_channels(struct mixer_build *state,
                                       struct uac_mixer_unit_descriptor *desc)
 {
-       int mu_channels;
+       int mu_channels = 0;
        void *c;
 
-       if (desc->bLength < sizeof(*desc))
-               return -EINVAL;
        if (!desc->bNrInPins)
                return -EINVAL;
-       if (desc->bLength < sizeof(*desc) + desc->bNrInPins)
-               return -EINVAL;
 
        switch (state->mixer->protocol) {
        case UAC_VERSION_1:
+               // limit derived from uac_mixer_unit_bmControls
+               if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 4)
+                       return 0;
+
+               mu_channels = uac_mixer_unit_bNrChannels(desc);
+               break;
+
        case UAC_VERSION_2:
-       default:
-               if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 1)
+               // limit derived from uac_mixer_unit_bmControls
+               if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 6)
                        return 0; /* no bmControls -> skip */
+
                mu_channels = uac_mixer_unit_bNrChannels(desc);
                break;
        case UAC_VERSION_3:
+               // limit derived from uac_mixer_unit_bmControls
+               if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 2)
+                       return 0; /* no bmControls -> skip */
+
                mu_channels = get_cluster_channels_v3(state,
                                uac3_mixer_unit_wClusterDescrID(desc));
                break;
+
+       default:
+               break;
        }
 
        if (!mu_channels)
-- 
2.22.1