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[PATCH 4.4 014/101] USB: gadgetfs: fix checks of wTotalLength in config descriptors

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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Alan Stern <stern@rowland.harvard.edu>

commit 1c069b057dcf64fada952eaa868d35f02bb0cfc2 upstream.

Andrey Konovalov's fuzz testing of gadgetfs showed that we should
improve the driver's checks for valid configuration descriptors passed
in by the user.  In particular, the driver needs to verify that the
wTotalLength value in the descriptor is not too short (smaller
than USB_DT_CONFIG_SIZE).  And the check for whether wTotalLength is
too large has to be changed, because the driver assumes there is
always enough room remaining in the buffer to hold a device descriptor
(at least USB_DT_DEVICE_SIZE bytes).

This patch adds the additional check and fixes the existing check.  It
may do a little more than strictly necessary, but one extra check
won't hurt.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/gadget/legacy/inode.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1755,10 +1755,12 @@ static struct usb_gadget_driver probe_dr
  * such as configuration notifications.
  */
 
-static int is_valid_config (struct usb_config_descriptor *config)
+static int is_valid_config(struct usb_config_descriptor *config,
+		unsigned int total)
 {
 	return config->bDescriptorType == USB_DT_CONFIG
 		&& config->bLength == USB_DT_CONFIG_SIZE
+		&& total >= USB_DT_CONFIG_SIZE
 		&& config->bConfigurationValue != 0
 		&& (config->bmAttributes & USB_CONFIG_ATT_ONE) != 0
 		&& (config->bmAttributes & USB_CONFIG_ATT_WAKEUP) == 0;
@@ -1808,7 +1810,8 @@ dev_config (struct file *fd, const char
 	/* full or low speed config */
 	dev->config = (void *) kbuf;
 	total = le16_to_cpu(dev->config->wTotalLength);
-	if (!is_valid_config (dev->config) || total >= length)
+	if (!is_valid_config(dev->config, total) ||
+			total > length - USB_DT_DEVICE_SIZE)
 		goto fail;
 	kbuf += total;
 	length -= total;
@@ -1817,7 +1820,8 @@ dev_config (struct file *fd, const char
 	if (kbuf [1] == USB_DT_CONFIG) {
 		dev->hs_config = (void *) kbuf;
 		total = le16_to_cpu(dev->hs_config->wTotalLength);
-		if (!is_valid_config (dev->hs_config) || total >= length)
+		if (!is_valid_config(dev->hs_config, total) ||
+				total > length - USB_DT_DEVICE_SIZE)
 			goto fail;
 		kbuf += total;
 		length -= total;

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[PATCH 4.4 000/101] 4.4.42-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 004/101] ARM: davinci: da850: dont add emac clock to lookup table twice Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 059/101] mei: bus: fix mei_cldev_enable KDoc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 026/101] usb: xhci: hold lock over xhci_abort_cmd_ring() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 051/101] usb: musb: Fix trying to free already-free IRQ 4 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 055/101] USB: serial: kl5kusb105: abort on open exception path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 043/101] USB: serial: mos7720: fix NULL-deref at open Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 020/101] xhci: workaround for hosts missing CAS bit Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 056/101] ARM: dts: r8a7794: Correct hsusb parent clock Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 005/101] mac80211: initialize fast-xmit info later Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 003/101] ALSA: usb-audio: Fix irq/process data synchronization Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:20 +0100
  [PATCH 4.4 013/101] USB: gadgetfs: fix use-after-free bug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 014/101] USB: gadgetfs: fix checks of wTotalLength in config descriptors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 019/101] usb: xhci: fix possible wild pointer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 001/101] ALSA: hda - Fix up GPIO for ASUS ROG Ranger Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 018/101] usb: dwc3: core: avoid Overflow events Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 011/101] usb: gadgetfs: restrict upper bound on device configuration size Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  [PATCH 4.4 015/101] USB: fix problems with duplicate endpoint addresses Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-10 16:30 +0100
  Re: [PATCH 4.4 000/101] 4.4.42-stable review Shuah Khan <shuah.kh@samsung.com> - 2017-01-10 18:40 +0100
  Re: [PATCH 4.4 000/101] 4.4.42-stable review Guenter Roeck <linux@roeck-us.net> - 2017-01-10 23:30 +0100

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