linux-kernel - [PATCH 1/2] Fix an OOB bug in parse_audio_mixer

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Date:   Fri, 30 Aug 2019 17:46:49 -0400
From:   Hui Peng <benquike@...il.com>
To:     stable@...r.kernel.org
Cc:     Hui Peng <benquike@...il.com>,
        Mathias Payer <mathias.payer@...elwelt.net>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Wenwen Wang <wang6495@....edu>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] Fix an OOB bug in parse_audio_mixer_unit

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.

CVE: CVE-2018-15117

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

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 1f7eb3816cd7..10ddec76f906 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1628,6 +1628,7 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid,
 	int pin, ich, err;
 
 	if (desc->bLength < 11 || !(input_pins = desc->bNrInPins) ||
+	    desc->bLength < sizeof(*desc) + desc->bNrInPins ||
 	    !(num_outs = uac_mixer_unit_bNrChannels(desc))) {
 		usb_audio_err(state->chip,
 			      "invalid MIXER UNIT descriptor %d\n",
-- 
2.17.1