[PATCH] PCI: Fix host bridge double put in pci_register_host_bridge()

[Nirmoy Das]

When device_register() fails for the root bus, the unregister path in
pci_register_host_bridge() drops a bridge reference with put_device()
and then releases the bus with put_device(&bus->dev). The bus release
callback, release_pcibus_dev(), also drops bus->bridge, so the bridge
loses two references for the one taken when the bus was set up.

This frees the host bridge before pci_register_host_bridge() returns.
The caller then drops its own reference on freed memory, either in
pci_create_root_bus() or in the devres action of
devm_pci_alloc_host_bridge().

KASAN reports the use after free in pci_host_probe() when the bus device
registration fails:

  BUG: KASAN: slab-use-after-free in pci_host_probe+0x17c/0x180
  Read of size 8 at addr ffff00000699d840 by task insmod/61
  Freed by task 61:
   kfree+0x274/0x4ec
   pci_release_host_bridge_dev+0x88/0xa4
   device_release+0x9c/0x1ec
   kobject_put+0x138/0x24c
   put_device+0x10/0x1c
   release_pcibus_dev+0x30/0x60
   device_release+0x9c/0x1ec
   kobject_put+0x138/0x24c
   put_device+0x10/0x1c
   pci_register_host_bridge+0x63c/0x1244
   pci_scan_root_bus_bridge+0x110/0x24c
   pci_host_probe+0x34/0x180
  refcount_t: underflow; use-after-free.

Tested on arm64 under QEMU/KVM with KASAN, using a test module that
occupies the pci_bus sysfs name so that device_register() of the root bus
fails with -EEXIST. With the fix, pci_host_probe() returns the error and
the devres teardown completes without KASAN or refcount warnings.

Fixes: 804443c1f278 ("PCI: Fix reference leak in pci_register_host_bridge()")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Nirmoy Das <nirmoyd@xxxxxxxxxx>
---
 drivers/pci/probe.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 9a178e0e5f7f467..86dbfd4873963e8 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1149,7 +1149,6 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 	return 0;
 
 unregister:
-	put_device(&bridge->dev);
 	device_del(&bridge->dev);
 free:
 #ifdef CONFIG_PCI_DOMAINS_GENERIC
-- 
2.43.0