CVE-2026-31578

Summary

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

media: as102: fix to not free memory after the device is registered in as102_usb_probe()

In as102_usb driver, the following race condition occurs:

		CPU0						CPU1
as102_usb_probe()
  kzalloc(); // alloc as102_dev_t
  ....
  usb_register_dev();
						fd = sys_open("/path/to/dev"); // open as102 fd
						....
  usb_deregister_dev();
  ....
  kfree(); // free as102_dev_t
  ....
						sys_close(fd);
						  as102_release() // UAF!!
						    as102_usb_release()
						      kfree(); // DFB!!

When a USB character device registered with usb_register_dev() is later unregistered (via usb_deregister_dev() or disconnect), the device node is removed so new open() calls fail. However, file descriptors that are already open do not go away immediately: they remain valid until the last reference is dropped and the driver's .release() is invoked.

In as102, as102_usb_probe() calls usb_register_dev() and then, on an error path, does usb_deregister_dev() and frees as102_dev_t right away. If userspace raced a successful open() before the deregistration, that open FD will later hit as102_release() –> as102_usb_release() and access or free as102_dev_t again, occur a race to use-after-free and double-free vuln.

The fix is to never kfree(as102_dev_t) directly once usb_register_dev() has succeeded. After deregistration, defer freeing memory to .release().

In other words, let release() perform the last kfree when the final open FD is closed.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/0d36653a3a821e5a974798adb347b3ea09332914
• https://git.kernel.org/stable/c/25d500cf391e384356a612b85cf60b353ad3cd0c
• https://git.kernel.org/stable/c/07ceb444c8f627cf863864d4274b5a77769725ed
• https://git.kernel.org/stable/c/cb8092038e95dc1113a68e63762de40fff61ba71
• https://git.kernel.org/stable/c/582fbecb3756330006fe1950762412a68c2cacd2
• https://git.kernel.org/stable/c/09e9206008b887aa553733bd915d73131071a086
• https://git.kernel.org/stable/c/2eeae47a438694408189138048a786be99954032
• https://git.kernel.org/stable/c/7e5aedf6059cba2a669d86caeaf5a51f33ec85a1
• https://git.kernel.org/stable/c/8bd29dbe03fc5b0f039ab2395ff37b64236d2f0c

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