CVE-2023-52855

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

usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency

In _dwc2_hcd_urb_enqueue(), urb->hcpriv = NULL is executed without holding the lock hsotg->lock. In _dwc2_hcd_urb_dequeue():

spin_lock_irqsave(&hsotg->lock, flags);
...
if (!urb->hcpriv) {
	dev_dbg(hsotg->dev, ## urb->hcpriv is NULL ##n);
	goto out;
}
rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv
...

out: spin_unlock_irqrestore(&hsotg->lock, flags);

When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are concurrently executed, the NULL check of urb->hcpriv can be executed before urb->hcpriv = NULL. After urb->hcpriv is NULL, it can be used in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL pointer dereference.

This possible bug is found by an experimental static analysis tool developed by myself. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations. The above possible bug is reported, when my tool analyzes the source code of Linux 6.5.

To fix this possible bug, urb->hcpriv = NULL should be executed with holding the lock hsotg->lock. After using this patch, my tool never reports the possible bug, with the kernelconfiguration allyesconfig for x86_64. Because I have no associated hardware, I cannot test the patch in runtime testing, and just verify it according to the code logic.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/14c9ec34e8118fbffd7f5431814d767726323e72
• https://git.kernel.org/stable/c/3e851a77a13ce944d703721793f49ee82622986d
• https://git.kernel.org/stable/c/64c47749fc7507ed732e155c958253968c1d275e
• https://git.kernel.org/stable/c/6b21a22728852d020a6658d39cd7bb7e14b07790
• https://git.kernel.org/stable/c/a7bee9598afb38004841a41dd8fe68c1faff4e90
• https://git.kernel.org/stable/c/bdb3dd4096302d6b87441fdc528439f171b04be6
• https://git.kernel.org/stable/c/ef307bc6ef04e8c1ea843231db58e3afaafa9fa6
• https://git.kernel.org/stable/c/fcaafb574fc88a52dce817f039f7ff2f9da38001
• https://git.kernel.org/stable/c/fed492aa6493a91a77ebd51da6fb939c98d94a0d