linux-kernel - [PATCH] PCI: ACPI: Check parent pointer in acpi_pci_find

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Message-ID: <5523582.DvuYhMxLoT@kreacher>
Date:   Fri, 01 Oct 2021 15:58:10 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Linux ACPI <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Shanker Donthineni <sdonthineni@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: [PATCH] PCI: ACPI: Check parent pointer in acpi_pci_find_companion()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

If acpi_pci_find_companion() is called for a device whose parent
pointer is NULL, it will crash when attempting to get the ACPI
companion of the parent due to a NULL pointer dereference in
the ACPI_COMPANION() macro.

This was not a problem before commit 375553a93201 ("PCI: Setup ACPI
fwnode early and at the same time with OF") that made pci_setup_device()
call pci_set_acpi_fwnode() and so it allowed devices with NULL parent
pointers to be passed to acpi_pci_find_companion() which is the case
in pci_iov_add_virtfn(), for instance.

Fix this issue by making acpi_pci_find_companion() check the device's
parent pointer upfront and bail out if it is NULL.

While pci_iov_add_virtfn() can be changed to set the device's parent
pointer before calling pci_setup_device() for it, checking pointers
against NULL before dereferencing them is prudent anyway and looking
for ACPI companions of virtual functions isn't really useful.

Fixes: 375553a93201 ("PCI: Setup ACPI fwnode early and at the same time with OF")
Link: https://lore.kernel.org/linux-acpi/8e4bbd5c59de31db71f718556654c0aa077df03d.camel@linux.ibm.com/
Reported-by: Niklas Schnelle <schnelle@...ux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@...ux.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/pci/pci-acpi.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-pm/drivers/pci/pci-acpi.c
===================================================================
--- linux-pm.orig/drivers/pci/pci-acpi.c
+++ linux-pm/drivers/pci/pci-acpi.c
@@ -1243,6 +1243,9 @@ static struct acpi_device *acpi_pci_find
 	bool check_children;
 	u64 addr;

+	if (!dev->parent)
+		return NULL;
+
 	down_read(&pci_acpi_companion_lookup_sem);

 	adev = pci_acpi_find_companion_hook ?