CVE-2021-46986

Summary

In the Linux kernel, the following vulnerability has been resolved:

usb: dwc3: gadget: Free gadget structure only after freeing endpoints

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().

Affected Software

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

• https://git.kernel.org/stable/c/1ea775021282d90e1d08d696b7ab54aa75d688e5
• https://git.kernel.org/stable/c/bc0cdd72493236fb72b390ad38ce581e353c143c
• https://git.kernel.org/stable/c/b4b8e9601d7ee8806d2687f081a42485d27674a1
• https://git.kernel.org/stable/c/bb9c74a5bd1462499fe5ccb1e3c5ac40dcfa9139

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: partial

References

• https://git.kernel.org/stable/c/1ea775021282d90e1d08d696b7ab54aa75d688e5
• https://git.kernel.org/stable/c/bc0cdd72493236fb72b390ad38ce581e353c143c
• https://git.kernel.org/stable/c/b4b8e9601d7ee8806d2687f081a42485d27674a1
• https://git.kernel.org/stable/c/bb9c74a5bd1462499fe5ccb1e3c5ac40dcfa9139

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