[PATCH 4.4 16/39] usb: gadget: f_fs: Use local copy of descriptors for userspace copy

[Greg Kroah-Hartman]

From: Vamsi Krishna Samavedam <vskrishn@xxxxxxxxxxxxxx>

commit a4b98a7512f18534ce33a7e98e49115af59ffa00 upstream.

The function may be unbound causing the ffs_ep and its descriptors
to be freed while userspace is in the middle of an ioctl requesting
the same descriptors. Avoid dangling pointer reference by first
making a local copy of desctiptors before releasing the spinlock.

Fixes: c559a3534109 ("usb: gadget: f_fs: add ioctl returning ep descriptor")
Reviewed-by: Peter Chen <peter.chen@xxxxxxx>
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@xxxxxxxxxxxxxx>
Signed-off-by: Jack Pham <jackp@xxxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201130203453.28154-1-jackp@xxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/gadget/function/f_fs.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -1034,7 +1034,7 @@ static long ffs_epfile_ioctl(struct file
 		case FUNCTIONFS_ENDPOINT_DESC:
 		{
 			int desc_idx;
-			struct usb_endpoint_descriptor *desc;
+			struct usb_endpoint_descriptor desc1, *desc;
 
 			switch (epfile->ffs->gadget->speed) {
 			case USB_SPEED_SUPER:
@@ -1046,10 +1046,12 @@ static long ffs_epfile_ioctl(struct file
 			default:
 				desc_idx = 0;
 			}
+
 			desc = epfile->ep->descs[desc_idx];
+			memcpy(&desc1, desc, desc->bLength);
 
 			spin_unlock_irq(&epfile->ffs->eps_lock);
-			ret = copy_to_user((void *)value, desc, sizeof(*desc));
+			ret = copy_to_user((void *)value, &desc1, desc1.bLength);
 			if (ret)
 				ret = -EFAULT;
 			return ret;