In function pci_scan_bridge_extend(), if the variable next_busnr gets to 256, "child = pci_find_bus()" will return bus 0 (root bus). Consequently, we have a circular PCI topology. The scan will then go in circle until the kernel crashes due to stack overflow.

This can be reproduced with: qemu-system-x86_64 -machine pc-q35-2.10 \ -kernel bzImage \ -m 2048 -smp 1 -enable-kvm \ -append "console=ttyS0 root=/dev/sda debug" \ -nographic \ -device pcie-root-port,bus=pcie.0,slot=1,id=rp1,bus-reserve=253 \ -device pcie-root-port,bus=pcie.0,slot=2,id=rp2,bus-reserve=0 \ -device pcie-root-port,bus=pcie.0,slot=3,id=rp3,bus-reserve=0

Check if next_busnr "overflow" and bail out if this is the case.

Signed-off-by: Nam Cao namcao@linutronix.de Cc: stable@vger.kernel.org # all --- This bug exists since the beginning of git history. So I didn't bother tracing beyond git to see which patch introduced this. --- drivers/pci/probe.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 1325fbae2f28..03caae76337c 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -1382,6 +1382,9 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev, else next_busnr = max + 1;

+ if (next_busnr == 256) + goto out; + /* * Prevent assigning a bus number that already exists. * This can happen when a bridge is hot-plugged, so in this