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Subject[PATCH] Fix an OOB bug in parse_audio_mixer_unit
Date
The `uac_mixer_unit_descriptor` shown as below is read from the
device side. In `parse_audio_mixer_unit`, `baSourceID` field is
accessed from index 0 to `bNrInPins` - 1, the current implementation
assumes that descriptor is always valid (the length of descriptor
is no shorter than 5 + `bNrInPins`). If a descriptor read from
the device side is invalid, it may trigger out-of-bound memory
access.

```
struct uac_mixer_unit_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bDescriptorSubtype;
__u8 bUnitID;
__u8 bNrInPins;
__u8 baSourceID[];
}
```

This patch fixes the bug by add a sanity check on the length of
the descriptor.

Signed-off-by: Hui Peng <benquike@gmail.com>
Reported-by: Hui Peng <benquike@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
---
sound/usb/mixer.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 7498b5191b68..38202ce67237 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2091,6 +2091,15 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid,
struct usb_audio_term iterm;
int input_pins, num_ins, num_outs;
int pin, ich, err;
+ int desc_len = (int) ((unsigned long) state->buffer +
+ state->buflen - (unsigned long) raw_desc);
+
+ if (desc_len < sizeof(*desc) + desc->bNrInPins) {
+ usb_audio_err(state->chip,
+ "descriptor %d too short\n",
+ unitid);
+ return -EINVAL;
+ }

err = uac_mixer_unit_get_channels(state, desc);
if (err < 0) {
--
2.22.1
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