ata: pata_parport: fix UAF on protocol module unload

This series fixes use-after-free issues in pata_parport when a protocol module goes away while pi_adapter devices created by it are still attached.

Patch 1 pins the protocol module before the device becomes visible. Previously try_module_get() ran after device_register(), so a forced module unload in between left pi->proto dangling from the moment the device appeared on the bus.

Patch 2 makes pata_parport_unregister_driver() tear down all adapters using the protocol. Without this, the rollback path of a multi-protocol module init (e.g. kbic registering k951 then k971) left the devices of the already-registered protocol alive while the module loader freed the module memory; removing such a dangling device later crashed in pi_disconnect() dereferencing pi->proto->disconnect.

Pei Xiao (2):
ata: pata_parport: pin the protocol module before device_register()
ata: pata_parport: unregister devices on protocol unregister

 drivers/ata/pata_parport/pata_parport.c | 28 ++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

2.25.1

pi_init_one() calls device_register() before try_module_get(). Between these two calls the device is already visible but the module is not pinned yet, so an unload in this window leaves pi->proto dangling:

pi_init_one() rmmod -f <proto>
--------------------------------------------------------
device_register(&pi->dev)
device visible on the bus
module memory freed
pi->proto = pr <- writes into freed memory / dangles
try_module_get(...) <- too late, module already gone

Take the module reference before registering the device, and drop it on the device_register() failure path.

---
changes in v2:
1.remove out_unreg_dev: label

---
 drivers/ata/pata_parport/pata_parport.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

index cf81a6128f55..046ab7e3adbc 100644
@@ -509,6 +509,14 @@ static struct pi_adapter *pi_init_one(struct parport *parport,
 		return NULL;
 	}
 
+	pi->proto = pr;
+
+	if (!try_module_get(pi->proto->owner)) {
+		kfree(pi);
+		ida_free(&pata_parport_bus_dev_ids, id);
+		return NULL;
+	}
+
 	/* set up pi->dev before pi_probe_unit() so it can use dev_printk() */
 	pi->dev.parent = pata_parport_bus;
 	pi->dev.bus = &pata_parport_bus_type;

@@ -517,15 +525,12 @@ static struct pi_adapter *pi_init_one(struct parport *parport,
 	pi->dev.id = id;
 	dev_set_name(&pi->dev, "pata_parport.%u", pi->dev.id);
 	if (device_register(&pi->dev)) {
+		module_put(pi->proto->owner);
 		put_device(&pi->dev);
 		/* pata_parport_dev_release will do ida_free(dev->id) and kfree(pi) */
 		return NULL;
 	}
 
-	pi->proto = pr;
-
-	if (!try_module_get(pi->proto->owner))
-		goto out_unreg_dev;
 	if (pi->proto->init_proto && pi->proto->init_proto(pi) < 0)
 		goto out_module_put;
 

@@ -568,7 +573,6 @@ static struct pi_adapter *pi_init_one(struct parport *parport,
 		pi->proto->release_proto(pi);
 out_module_put:
 	module_put(pi->proto->owner);
-out_unreg_dev:
 	device_unregister(&pi->dev);
 	/* pata_parport_dev_release will do ida_free(dev->id) and kfree(pi) */
 	return NULL;

2.25.1

When a protocol module registers multiple protocols and a later registration fails (e.g. kbic_init registering k951 then k971), the rollback path calls pata_parport_unregister_driver() on the already registered protocol. This removes the protocol from the IDR and unregisters the driver, but leaves the dynamically created pi_adapter devices untouched.

Since the module init then fails, the module loader frees the module memory, bypassing the references held by the devices. Any later removal of these dangling devices (e.g. via sysfs delete_device or parport detach) hits pi_remove_one() -> pi_disconnect() -> pi->proto->disconnect, dereferencing the freed module memory and crashing the kernel.

Tear down all pi_adapters using the protocol in pata_parport_unregister_driver(), before driver_unregister(), while the module is still alive so the ->disconnect / ->release_proto callbacks are safe to call.

---
 drivers/ata/pata_parport/pata_parport.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index 046ab7e3adbc..712209882ab7 100644
@@ -611,6 +611,18 @@ int pata_parport_register_driver(struct pi_protocol *pr)
 }
 EXPORT_SYMBOL_GPL(pata_parport_register_driver);
 
+static int pi_remove_by_proto(struct device *dev, void *data)
+{
+	struct pi_protocol *pr = data;
+	struct ata_host *host = dev_get_drvdata(dev);
+	struct pi_adapter *pi = host->private_data;
+
+	if (pi->proto == pr)
+		pi_remove_one(dev);
+
+	return 0;
+}
+
 void pata_parport_unregister_driver(struct pi_protocol *pr)
 {
 	struct pi_protocol *pr_iter;

@@ -622,6 +634,8 @@ void pata_parport_unregister_driver(struct pi_protocol *pr)
 			break;
 	}
 	idr_remove(&protocols, id);
+	/* remove adapters using this protocol while the module is still alive */
+	bus_for_each_dev(&pata_parport_bus_type, NULL, pr, pi_remove_by_proto);
 	driver_unregister(&pr->driver);
 	mutex_unlock(&pi_mutex);
 

2.25.1

Looking at idr_alloc(), this looks like a legit pre-existing issue.

There is another call to idr_alloc() i pata_parport_register_driver(), but it does:
error = idr_alloc(&protocols, pr, 0, 0, GFP_KERNEL);

0,0 is start,end

if @end is <= 0, it is treated as one larger than %INT_MAX

So this is only a problem in pata_parport_attach().

Kind regards,
Niklas

Applied to libata/linux.git (for-7.4), thanks!

[1/2] ata: pata_parport: pin the protocol module before device_register()

      https://git.kernel.org/libata/linux/c/5d3355c7
[2/2] ata: pata_parport: unregister devices on protocol unregister
      https://git.kernel.org/libata/linux/c/d82c5cf6

Kind regards,
Niklas

This series was dropped because of kernel test robot reporting build error.

(Interestingly, Sashiko did only reported an unrelated pre-existing issue, but did not report the build error.)

Kind regards,
Niklas