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Subject[PATCH 3.16 007/202] ALSA: usb-audio: Always check descriptor sizes in parser code
3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Takashi Iwai <tiwai@suse.de>

commit 3e96d7280f16e2f787307f695a31296b9e4a1cd7 upstream.

There are a few places where we access the data without checking the
actual object size from the USB audio descriptor. This may result in
OOB access, as recently reported.

This patch addresses these missing checks. Most of added codes are
simple bLength checks in the caller side. For the input and output
terminal parsers, we put the length check in the parser functions.
For the input terminal, a new argument is added to distinguish between
UAC1 and the rest, as they treat different objects.

Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Reported-by: Hui Peng <benquike@163.com>
Tested-by: Hui Peng <benquike@163.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16:
- Drop changes in parse_audio_input_terminal() and UAC3 handling
- Adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -258,6 +258,11 @@ static int snd_usb_create_streams(struct
return -EINVAL;
}

+ if (h1->bLength < sizeof(*h1)) {
+ dev_err(&dev->dev, "cannot find UAC_HEADER\n");
+ return -EINVAL;
+ }
+
if (!h1->bInCollection) {
dev_info(&dev->dev, "skipping empty audio interface (v1)\n");
return -EINVAL;
--- a/sound/usb/stream.c
+++ b/sound/usb/stream.c
@@ -412,12 +412,8 @@ static int parse_uac_endpoint_attributes
csep = snd_usb_find_desc(alts->extra, alts->extralen, NULL, USB_DT_CS_ENDPOINT);

if (!csep || csep->bLength < 7 ||
- csep->bDescriptorSubtype != UAC_EP_GENERAL) {
- usb_audio_warn(chip,
- "%u:%d : no or invalid class specific endpoint descriptor\n",
- iface_no, altsd->bAlternateSetting);
- return 0;
- }
+ csep->bDescriptorSubtype != UAC_EP_GENERAL)
+ goto error;

if (protocol == UAC_VERSION_1) {
attributes = csep->bmAttributes;
@@ -425,6 +421,8 @@ static int parse_uac_endpoint_attributes
struct uac2_iso_endpoint_descriptor *csep2 =
(struct uac2_iso_endpoint_descriptor *) csep;

+ if (csep2->bLength < sizeof(*csep2))
+ goto error;
attributes = csep->bmAttributes & UAC_EP_CS_ATTR_FILL_MAX;

/* emulate the endpoint attributes of a v1 device */
@@ -433,6 +431,12 @@ static int parse_uac_endpoint_attributes
}

return attributes;
+
+ error:
+ usb_audio_warn(chip,
+ "%u:%d : no or invalid class specific endpoint descriptor\n",
+ iface_no, altsd->bAlternateSetting);
+ return 0;
}

/* find an input terminal descriptor (either UAC1 or UAC2) with the given
@@ -440,13 +444,17 @@ static int parse_uac_endpoint_attributes
*/
static void *
snd_usb_find_input_terminal_descriptor(struct usb_host_interface *ctrl_iface,
- int terminal_id)
+ int terminal_id, bool uac2)
{
struct uac2_input_terminal_descriptor *term = NULL;
+ size_t minlen = uac2 ? sizeof(struct uac2_input_terminal_descriptor) :
+ sizeof(struct uac_input_terminal_descriptor);

while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
ctrl_iface->extralen,
term, UAC_INPUT_TERMINAL))) {
+ if (term->bLength < minlen)
+ continue;
if (term->bTerminalID == terminal_id)
return term;
}
@@ -463,7 +471,8 @@ static struct uac2_output_terminal_descr
while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
ctrl_iface->extralen,
term, UAC_OUTPUT_TERMINAL))) {
- if (term->bTerminalID == terminal_id)
+ if (term->bLength >= sizeof(*term) &&
+ term->bTerminalID == terminal_id)
return term;
}

@@ -561,7 +570,8 @@ int snd_usb_parse_audio_interface(struct
format = le16_to_cpu(as->wFormatTag); /* remember the format value */

iterm = snd_usb_find_input_terminal_descriptor(chip->ctrl_intf,
- as->bTerminalLink);
+ as->bTerminalLink,
+ false);
if (iterm) {
num_channels = iterm->bNrChannels;
chconfig = le16_to_cpu(iterm->wChannelConfig);
@@ -597,7 +607,8 @@ int snd_usb_parse_audio_interface(struct
/* lookup the terminal associated to this interface
* to extract the clock */
input_term = snd_usb_find_input_terminal_descriptor(chip->ctrl_intf,
- as->bTerminalLink);
+ as->bTerminalLink,
+ true);
if (input_term) {
clock = input_term->bCSourceID;
if (!chconfig && (num_channels == input_term->bNrChannels))
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