USB: handle NULL config in usb_find_alt_setting()

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@rowland.harvard.edu>
Reported-by: syzbot+19c3aaef85a89d451eac@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 623be3174fb3..79d8bd7a612e 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -228,6 +228,8 @@ struct usb_host_interface *usb_find_alt_setting(
         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) {