Re: [PATCH] perf/dwc_pcie: Fix PCI device reference leak in probe

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

Pre-existing issues:
- [High] The PMU driver stores a pointer to the PCI device (`pdev`) without retaining a reference, exposing the system to a Use-After-Free (UAF) if the PCI device is hot-removed.
- [High] Concurrent modification of the global dwc_pcie_dev_info_head list without locking.
--

--- Patch [1]: [PATCH] perf/dwc_pcie: Fix PCI device reference leak in probe ---
commit 2589eb488a31451ac7fb41c9454a6b4efd3a7453
Author: Ruoyu Wang <[email protected]>

perf/dwc_pcie: Fix PCI device reference leak in probe

This commit addresses a PCI device reference leak when the subsequent RAS
DES capability lookup fails. It moves the pci_dev_put call immediately
after capability discovery to release the reference on both success and
failure paths.

> diff --git a/drivers/perf/dwc_pcie_pmu.c b/drivers/perf/dwc_pcie_pmu.c
> index 6b9ed59de26eb..976e09f0d81b7 100644
> --- a/drivers/perf/dwc_pcie_pmu.c
> +++ b/drivers/perf/dwc_pcie_pmu.c
> @@ -763,10 +763,10 @@ static int dwc_pcie_pmu_probe(struct platform_device *plat_dev)
>  	}
>  
>  	vsec = dwc_pcie_des_cap(pdev);
> +	pci_dev_put(pdev);

[Severity: High]
This is a pre-existing issue, but I have a question about how the PCI device
reference is managed here.

Since pci_dev_put(pdev) is called to drop the reference, is it safe to
subsequently store and dereference this pointer?

In drivers/perf/dwc_pcie_pmu.c:dwc_pcie_pmu_probe(), the pdev pointer is
stored in the PMU structure:

	pcie_pmu->pdev = pdev;

If the PCI device is hot-removed during the initialization window before the
bus notifier is registered in dwc_pcie_pmu_init(), the BUS_NOTIFY_DEL_DEVICE
event could be missed. This would mean the PMU platform device is never
unregistered, and the PCI subsystem would free the struct pci_dev.

Could this leave pcie_pmu->pdev pointing to freed memory, leading to a
use-after-free when subsequent PMU operations or CPU hotplug callbacks like
dwc_pcie_pmu_online_cpu() access it?

>  	if (!vsec)
>  		return -ENODEV;
>  
> -	pci_dev_put(pdev);
>  	name = devm_kasprintf(&plat_dev->dev, GFP_KERNEL, "dwc_rootport_%x", sbdf);

[ ... ]

[Severity: High]
This is a pre-existing issue, but can the global linked list be corrupted
if multiple PCI devices are hot-plugged concurrently?

In drivers/perf/dwc_pcie_pmu.c, the global list dwc_pcie_dev_info_head is
modified without acquiring a lock:

dwc_pcie_register_dev() {
...
	list_add(&dev_info->dev_node, &dwc_pcie_dev_info_head);
...
}

dwc_pcie_unregister_dev() {
...
	list_del(&dev_info->dev_node);
...
}

These functions are invoked by the driver's PCI bus notifier
(dwc_pcie_pmu_nb) responding to BUS_NOTIFY_ADD_DEVICE and
BUS_NOTIFY_DEL_DEVICE events.

Since the driver core's bus notifier chain uses a read-write semaphore
which allows concurrent hotplug events across different devices to invoke
notifiers simultaneously, couldn't this trigger a data race on list_add
and list_del?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=1