CVE-2021-46986 usb: dwc3: gadget: Free gadget structure only after freeing endpoints

2024-02-2808:13:14

Linux

www.cve.org

linux kernel

dwc3 gadget

free gadget structure

use-after-free

kasan

driver unbind

shutdown panic

usb_del_gadget_udc

dwc3_gadget_free_endpoints

6.6 Medium

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

15.7%

JSON

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().

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/usb/dwc3/gadget.c"
    ],
    "versions": [
      {
        "version": "e81a7018d93a",
        "lessThan": "1ea775021282",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "e81a7018d93a",
        "lessThan": "bc0cdd724932",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "e81a7018d93a",
        "lessThan": "b4b8e9601d7e",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "e81a7018d93a",
        "lessThan": "bb9c74a5bd14",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/usb/dwc3/gadget.c"
    ],
    "versions": [
      {
        "version": "5.10",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "5.10",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.38",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.11.22",
        "lessThanOrEqual": "5.11.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.12.5",
        "lessThanOrEqual": "5.12.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.13",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]