[PATCH 4.9 65/94] USB: handle NULL config in usb_find_alt_setting()

[Greg Kroah-Hartman]

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

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

From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

commit c9a4cb204e9eb7fa7dfbe3f7d3a674fa530aa193 upstream.

usb_find_alt_setting() takes a pointer to a struct usb_host_config as
an argument; it searches for an interface with specified interface and
alternate setting numbers in that config.  However, it crashes if the
usb_host_config pointer argument is NULL.

Since this is a general-purpose routine, available for use in many
places, we want to to be more robust.  This patch makes it return NULL
whenever the config argument is NULL.

Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot+19c3aaef85a89d451eac@xxxxxxxxxxxxxxxxxxxxxxxxx
CC: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/core/usb.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -91,6 +91,8 @@ struct usb_host_interface *usb_find_alt_
 	struct usb_interface_cache *intf_cache = NULL;
 	int i;
 
+	if (!config)
+		return NULL;
 	for (i = 0; i < config->desc.bNumInterfaces; i++) {
 		if (config->intf_cache[i]->altsetting[0].desc.bInterfaceNumber
 				== iface_num) {