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Subject[PATCH 4.19 106/148] ALSA: usb-audio: Check mixer unit descriptors more strictly
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

commit 0bfe5e434e6665b3590575ec3c5e4f86a1ce51c9 upstream.

We've had some sanity checks of the mixer unit descriptors but they
are too loose and some corner cases are overlooked. Add more strict
checks in uac_mixer_unit_get_channels() for avoiding possible OOB
accesses by malformed descriptors.

This also changes the semantics of uac_mixer_unit_get_channels()
slightly. Now it returns zero for the cases where the descriptor
lacks of bmControls instead of -EINVAL. Then the caller side skips
the mixer creation for such unit while it keeps parsing it.
This corresponds to the case like Maya44.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/usb/mixer.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -753,8 +753,9 @@ static int uac_mixer_unit_get_channels(s
struct uac_mixer_unit_descriptor *desc)
{
int mu_channels;
+ void *c;

- if (desc->bLength < 11)
+ if (desc->bLength < sizeof(*desc))
return -EINVAL;
if (!desc->bNrInPins)
return -EINVAL;
@@ -763,6 +764,8 @@ static int uac_mixer_unit_get_channels(s
case UAC_VERSION_1:
case UAC_VERSION_2:
default:
+ if (desc->bLength < sizeof(*desc) + desc->bNrInPins + 1)
+ return 0; /* no bmControls -> skip */
mu_channels = uac_mixer_unit_bNrChannels(desc);
break;
case UAC_VERSION_3:
@@ -772,7 +775,11 @@ static int uac_mixer_unit_get_channels(s
}

if (!mu_channels)
- return -EINVAL;
+ return 0;
+
+ c = uac_mixer_unit_bmControls(desc, state->mixer->protocol);
+ if (c - (void *)desc + (mu_channels - 1) / 8 >= desc->bLength)
+ return 0; /* no bmControls -> skip */

return mu_channels;
}
@@ -944,7 +951,7 @@ static int check_input_term(struct mixer
struct uac_mixer_unit_descriptor *d = p1;

err = uac_mixer_unit_get_channels(state, d);
- if (err < 0)
+ if (err <= 0)
return err;

term->channels = err;
@@ -2118,7 +2125,7 @@ static int parse_audio_mixer_unit(struct
if (err < 0)
continue;
/* no bmControls field (e.g. Maya44) -> ignore */
- if (desc->bLength <= 10 + input_pins)
+ if (!num_outs)
continue;
err = check_input_term(state, desc->baSourceID[pin], &iterm);
if (err < 0)

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