[PATCH rtw-next] wifi: rtw88: check for PCI upstream bridge existence

[Fedor Pchelkin]

pci_upstream_bridge() returns NULL if the device is on a root bus.  If
8821CE is installed in the system with such a PCI topology, the probing
routine will crash.  This has probably been unnoticed as 8821CE is mostly
supplied in laptops where there is a PCI-to-PCI bridge located upstream
from the device.  However the card might be installed on a system with
different configuration.

Check if the bridge does exist for the specific workaround to be applied.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: 24f5e38a13b5 ("rtw88: Disable PCIe ASPM while doing NAPI poll on 8821CE")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
---

I don't have 8821CE but 8822CE instead and I've been able to reproduce the
NULL bridge pointer dereference with rtwdev->chip->id manually adjusted in
the workaround.  Wifi devices happen to be located on a root bus in most
of the systems I have access to.

 drivers/net/wireless/realtek/rtw88/pci.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
index 56b16186d3aa..ec0a45bfb670 100644
--- a/drivers/net/wireless/realtek/rtw88/pci.c
+++ b/drivers/net/wireless/realtek/rtw88/pci.c
@@ -1804,7 +1804,8 @@ int rtw_pci_probe(struct pci_dev *pdev,
 	}
 
 	/* Disable PCIe ASPM L1 while doing NAPI poll for 8821CE */
-	if (rtwdev->chip->id == RTW_CHIP_TYPE_8821C && bridge->vendor == PCI_VENDOR_ID_INTEL)
+	if (rtwdev->chip->id == RTW_CHIP_TYPE_8821C &&
+	    bridge && bridge->vendor == PCI_VENDOR_ID_INTEL)
 		rtwpci->rx_no_aspm = true;
 
 	rtw_pci_phy_cfg(rtwdev);
-- 
2.51.0