[PATCH v2] usb: dwc3: gadget: Free gadget structure only after freeing endpoints

[Jack Pham <jackp@codeaurora.org>]

As part of commit e81a7018d93a ("usb: dwc3: allocate gadget structure
dynamically") the dwc3_gadget_release() was added which will free
the dwc->gadget structure upon the device's removal when
usb_del_gadget_udc() is called in dwc3_gadget_exit().

However, simply freeing the gadget results a dangling pointer
situation: the endpoints created in dwc3_gadget_init_endpoints()
have their dep->endpoint.ep_list members chained off the list_head
anchored at dwc->gadget->ep_list.  Thus when dwc->gadget is freed,
the first dwc3_ep in the list now has a dangling prev pointer and
likewise for the next pointer of the dwc3_ep at the tail of the list.
The dwc3_gadget_free_endpoints() that follows will result in a
use-after-free when it calls list_del().

This was caught by enabling KASAN and performing a driver unbind.
The recent commit 568262bf5492 ("usb: dwc3: core: Add shutdown
callback for dwc3") also exposes this as a panic during shutdown.

There are a few possibilities to fix this.  One could be to perform
a list_del() of the gadget->ep_list itself which removes it from
the rest of the dwc3_ep chain.

Another approach is what this patch does, by splitting up the
usb_del_gadget_udc() call into its separate "del" and "put"
components.  This allows dwc3_gadget_free_endpoints() to be
called before the gadget is finally freed with usb_put_gadget().

Fixes: e81a7018d93a ("usb: dwc3: allocate gadget structure dynamically")
Signed-off-by: Jack Pham <jackp@codeaurora.org>
---
v2: Fix silly typo: usb_del_gadget_put -> usb_put_gadget (brain fart
when manually recomposing the patch)

 drivers/usb/dwc3/gadget.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 6eab78f8a1a7..c7e5f5a07f3b 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -4062,8 +4062,9 @@ int dwc3_gadget_init(struct dwc3 *dwc)
 
 void dwc3_gadget_exit(struct dwc3 *dwc)
 {
-	usb_del_gadget_udc(dwc->gadget);
+	usb_del_gadget(dwc->gadget);
 	dwc3_gadget_free_endpoints(dwc);
+	usb_put_gadget(dwc->gadget);
 	dma_free_coherent(dwc->sysdev, DWC3_BOUNCE_SIZE, dwc->bounce,
 			  dwc->bounce_addr);
 	kfree(dwc->setup_buf);
-- 
2.24.0