[PATCH] PCI: Fix pci_alloc_child_bus() error path

[Hans Zhang]

If device_register() fails in pci_alloc_child_bus(), put_device()
frees the child bus, but bridge->subordinate and the bridge resource
names still point into the freed child.  Subsequent rescans can then
dereference dangling pointers.

Also, WARN_ON(ret < 0) reports device_register() failures as a kernel
bug even when they are caused by normal runtime resource exhaustion,
such as fault-injected -ENOMEM.

Defer assigning bridge->subordinate and the bridge resource names until
after device_register() succeeds, and handle the error without WARN_ON().

Reported-by: syzbot+ea7278bdcb20a491495b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=ea7278bdcb20a491495b
Fixes: 4f535093cf8f6 ("PCI: Put pci_dev in device tree as early as possible")
Assisted-by: Codex:deepseek-v4-flash
Signed-off-by: Hans Zhang <18255117159@xxxxxxx>
---
 drivers/pci/probe.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 9a178e0e5f7f..0f317d25a32b 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1259,21 +1259,29 @@ static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
 		pci_info(child, "extended config space not accessible\n");
 	}
 
-	/* Set up default resource pointers and names */
-	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {
+	/*
+	 * Set up default resource pointers now, but defer pointing the bridge
+	 * resources at child->name until device_register() succeeds.  On
+	 * failure put_device() frees child, so any references to child would
+	 * otherwise dangle.
+	 */
+	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++)
 		child->resource[i] = &bridge->resource[PCI_BRIDGE_RESOURCES+i];
-		child->resource[i]->name = child->name;
-	}
-	bridge->subordinate = child;
 
 add_dev:
 	pci_set_bus_msi_domain(child);
 	ret = device_register(&child->dev);
-	if (WARN_ON(ret < 0)) {
+	if (ret < 0) {
 		put_device(&child->dev);
 		return NULL;
 	}
 
+	if (bridge) {
+		for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++)
+			child->resource[i]->name = child->name;
+		bridge->subordinate = child;
+	}
+
 	pcibios_add_bus(child);
 
 	if (child->ops->add_bus) {

base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
-- 
2.43.0