Re: [PATCH 1/2] misc: pci_endpoint_test: Fix doorbell success logic

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] Missing validation of device-supplied BAR and offset allows arbitrary out-of-bounds memory write and NULL pointer dereference.
- [High] Use-after-free and race condition in device removal due to improper teardown ordering.
--

--- Patch [1]: [PATCH 1/2] misc: pci_endpoint_test: Fix doorbell success logic ---
commit fca8adde489026db6a363f41e32f957940be89f4
Author: Niklas Cassel <cassel@kernel.org>

misc: pci_endpoint_test: Fix doorbell success logic

This patch modifies the pci_endpoint_test_doorbell function to ensure
that if triggering the doorbell fails, the test stores the error code
but continues on to disable the doorbell rather than returning early.

> diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> index 3635741c3e7a7..26ab9252251f1 100644
> --- a/drivers/misc/pci_endpoint_test.c
> +++ b/drivers/misc/pci_endpoint_test.c
> @@ -1071,6 +1071,7 @@ static int pci_endpoint_test_doorbell(struct pci_endpoint_test *test)
>  	struct pci_dev *pdev = test->pdev;
>  	struct device *dev = &pdev->dev;
>  	int irq_type = test->irq_type;
> +	int ret = 0;
>  	enum pci_barno bar;
>  	u32 data, status;
>  	u32 addr;
> @@ -1119,8 +1120,11 @@ static int pci_endpoint_test_doorbell(struct pci_endpoint_test *test)

[Severity: High]
This is a pre-existing issue, but since we are modifying the error handling
in pci_endpoint_test_doorbell(), is there an out-of-bounds write or NULL
pointer dereference possible just above this diff?

A malicious or malfunctioning PCIe endpoint can supply arbitrary values for
addr and bar. The code checks if bar is within the enum bounds, but does
not check if test->bar[bar] is actually mapped (i.e., non-NULL), nor does
it bounds-check addr against the mapped BAR's size before calling:

    writel(data, test->bar[bar] + addr);

Could this allow an arbitrary MMIO write to kernel space?

>  	status = pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_STATUS);
>  
> -	if (!left || !(status & STATUS_DOORBELL_SUCCESS))
> +	if (!left || !(status & STATUS_DOORBELL_SUCCESS)) {
>  		dev_err(dev, "Failed to trigger doorbell in endpoint\n");
> +		/* Store error code, but continue to disable doorbell. */
> +		ret = -EINVAL;
> +	}
>  
>  	pci_endpoint_test_writel(test, PCI_ENDPOINT_TEST_COMMAND,
>  				 COMMAND_DISABLE_DOORBELL);
> @@ -1134,10 +1138,7 @@ static int pci_endpoint_test_doorbell(struct pci_endpoint_test *test)
>  		return -EINVAL;
>  	}
>  
> -	if (!(status & STATUS_DOORBELL_SUCCESS))
> -		return -EINVAL;
> -
> -	return 0;
> +	return ret;
>  }
>  
>  static long pci_endpoint_test_ioctl(struct file *file, unsigned int cmd,

[Severity: High]
This isn't a bug introduced by this patch, but looking at how ioctls are
handled here, is there a use-after-free race condition during device
removal?

If a PCIe hot-unplug event or driver unbind occurs while a userspace
process is executing an ioctl, pci_endpoint_test_remove() will execute
concurrently:

    pci_endpoint_test_release_irq(test);
    pci_endpoint_test_free_irq_vectors(test);
    misc_deregister(&test->miscdev);

misc_deregister() does not wait for existing active file operations to
complete. Because the test struct is managed by devm_kzalloc(), it is freed
immediately after remove() returns.

Could the concurrent ioctl handler:

    mutex_lock(&test->mutex);

access the freed test memory or interact with torn-down IRQs or MMIO
regions? Does the driver need to synchronize device teardown with active
ioctls?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260730122045.1382749-4-cassel@kernel.org?part=1