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[X/B,SRU,CVE-2019-15117,1/2] ALSA: usb-audio: Fix an OOB bug in parse_audio_mixer_unit

Message ID 20190830001351.3686-4-connor.kuehl@canonical.com
State New
Headers show
Series [X/B,SRU,CVE-2019-15117,1/2] ALSA: usb-audio: Fix an OOB bug in parse_audio_mixer_unit | expand

Commit Message

Connor Kuehl Aug. 30, 2019, 12:13 a.m. UTC 
From: Hui Peng <benquike@gmail.com>

CVE-2019-15117

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.

Reported-by: Hui Peng <benquike@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Hui Peng <benquike@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
(backported from commit daac07156b330b18eb5071aec4b3ddca1c377f2c)
[ Connor Kuehl: this patch modifies uac_mixer_unit_get_channels()
  because that's where the error checking for parse_audio_mixer_unit()
  was relocated to in mainline commit 6cfd839ae78e "ALSA: usb-audio:
  UAC3. Add support for mixer unit." Instead of pulling that patch in
  so this one applies cleanly, I manually placed the new check in
  parse_audio_mixer_unit(). ]
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
---
 sound/usb/mixer.c | 1 +
 1 file changed, 1 insertion(+)
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Patch

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ee6871ebd936..713020741289 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1700,6 +1700,7 @@  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",