If a bridge is hot-added without any bus number available for its downstream bus, pci_hp_add_bridge() will fail. However, the driver proceeds regardless, and the kernel crashes.

This crash can be reproduced with the QEMU command: qemu-system-x86_64 -machine pc-q35-2.10 \ -kernel bzImage \ -drive "file=img,format=raw" \ -m 2048 -smp 2 -enable-kvm \ -append "console=ttyS0 root=/dev/sda" \ -nographic \ -device pcie-root-port,bus=pcie.0,id=rp1,slot=1,bus-reserve=0

then hot-plug a bridge at runtime with the QEMU command: device_add pcie-pci-bridge,id=br1,bus=rp1

and the kernel crashes:

pcieport 0000:00:03.0: pciehp: Slot(1): Button press: will power on in 5 sec pcieport 0000:00:03.0: pciehp: Slot(1): Card present pcieport 0000:00:03.0: pciehp: Slot(1): Link Up pci 0000:01:00.0: [1b36:000e] type 01 class 0x060400 PCIe to PCI/PCI-X bridge pci 0000:01:00.0: BAR 0 [mem 0x00000000-0x000000ff 64bit] pci 0000:01:00.0: PCI bridge to [bus 00] pci 0000:01:00.0: bridge window [io 0x0000-0x0fff] pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff] pci 0000:01:00.0: bridge window [mem 0x00000000-0x000fffff 64bit pref] pci 0000:01:00.0: No bus number available for hot-added bridge

(note: kernel should abort hot-plugging right here)

pci 0000:01:00.0: BAR 0 [mem 0xfe800000-0xfe8000ff 64bit]: assigned pcieport 0000:00:03.0: PCI bridge to [bus 01] pcieport 0000:00:03.0: bridge window [io 0x1000-0x1fff] pcieport 0000:00:03.0: bridge window [mem 0xfe800000-0xfe9fffff] pcieport 0000:00:03.0: bridge window [mem 0xfe000000-0xfe1fffff 64bit pref] shpchp 0000:01:00.0: HPC vendor_id 1b36 device_id e ss_vid 0 ss_did 0 shpchp 0000:01:00.0: enabling device (0000 -> 0002) BUG: kernel NULL pointer dereference, address: 00000000000000da PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 46 Comm: irq/24-pciehp Not tainted 6.9.0-rc1-00001-g2e0239d47d75 #33 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:shpc_init+0x3fb/0x9d0 [stack dump and register dump cut out]

Fix this by aborting the hot-plug if pci_hp_add_bridge() fails.

Fixes: 0eb3bcfd088e ("[PATCH] pciehp: allow bridged card hotplug") Signed-off-by: Nam Cao namcao@linutronix.de Cc: stable@vger.kernel.org --- v3: revert back to the solution in v1 (calling pci_stop_and_remove_bus_device() and returning negative error code)

v2: - remove "Cc: Rajesh Shah rajesh.shah@intel.com" (this address bounce) - add more information to commit message - return 0 instead of -EINVAL

drivers/pci/hotplug/pciehp_pci.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/hotplug/pciehp_pci.c b/drivers/pci/hotplug/pciehp_pci.c index ad12515a4a12..de783d7c8a16 100644 --- a/drivers/pci/hotplug/pciehp_pci.c +++ b/drivers/pci/hotplug/pciehp_pci.c @@ -59,7 +59,11 @@ int pciehp_configure_device(struct controller *ctrl) }

for_each_pci_bridge(dev, parent) - pci_hp_add_bridge(dev); + if (pci_hp_add_bridge(dev)) { + pci_stop_and_remove_bus_device(dev); + ret = -EINVAL; + goto out; + }

pci_assign_unassigned_bridge_resources(bridge); pcie_bus_configure_settings(parent);