[PATCH 3.16 108/157] USB: w1 ds2490: Fix bug caused by improper use of altsetting array

[Ben Hutchings]

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

commit c114944d7d67f24e71562fcfc18d550ab787e4d4 upstream.

The syzkaller USB fuzzer spotted a slab-out-of-bounds bug in the
ds2490 driver.  This bug is caused by improper use of the altsetting
array in the usb_interface structure (the array's entries are not
always stored in numerical order), combined with a naive assumption
that all interfaces probed by the driver will have the expected number
of altsettings.

The bug can be fixed by replacing references to the possibly
non-existent intf->altsetting[alt] entry with the guaranteed-to-exist
intf->cur_altsetting entry.

Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Reported-and-tested-by: syzbot+d65f673b847a1a96cdba@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/w1/masters/ds2490.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/w1/masters/ds2490.c
+++ b/drivers/w1/masters/ds2490.c
@@ -1041,15 +1041,15 @@ static int ds_probe(struct usb_interface
 	/* alternative 3, 1ms interrupt (greatly speeds search), 64 byte bulk */
 	alt = 3;
 	err = usb_set_interface(dev->udev,
-		intf->altsetting[alt].desc.bInterfaceNumber, alt);
+		intf->cur_altsetting->desc.bInterfaceNumber, alt);
 	if (err) {
 		dev_err(&dev->udev->dev, "Failed to set alternative setting %d "
 			"for %d interface: err=%d.\n", alt,
-			intf->altsetting[alt].desc.bInterfaceNumber, err);
+			intf->cur_altsetting->desc.bInterfaceNumber, err);
 		goto err_out_clear;
 	}
 
-	iface_desc = &intf->altsetting[alt];
+	iface_desc = intf->cur_altsetting;
 	if (iface_desc->desc.bNumEndpoints != NUM_EP-1) {
 		printk(KERN_INFO "Num endpoints=%d. It is not DS9490R.\n", iface_desc->desc.bNumEndpoints);
 		err = -EINVAL;