[PATCH 2/2] PCI: Fix pci_host_bridge struct device release/free handling

Rob Herring
2020-05-13T22:39:04Z

The PCI code has several paths where the struct pci_host_bridge is freed
directly. This is wrong because it contains a struct device which is
refcounted and should be freed using put_device(). This can result in
use-after-free errors. I think this problem has existed since 2012 with
commit 7b5436635800 ("PCI: add generic device into pci_host_bridge
struct"). It generally hasn't mattered as most host bridge drivers are
still built-in and can't unbind.

The problem is a struct device should never be freed directly once
device_initialize() is called and a ref is held, but that doesn't happen
until pci_register_host_bridge(). There's then a window between
allocating the host bridge and pci_register_host_bridge() where kfree
should be used. This is fragile and requires callers to do the right
thing. To fix this, we need to split device_register() into
device_initialize() and device_add() calls, so that the host bridge
struct is always freed by using a put_device().

devm_pci_alloc_host_bridge() is using devm_kzalloc() to allocate struct
pci_host_bridge which will be freed directly. Instead, we can use a
custom devres action to call put_device().

Reported-by: Anders Roxell <anders.roxell@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rob Herring <robh@kernel.org>
---
drivers/pci/probe.c | 36 +++++++++++++++++++-----------------
drivers/pci/remove.c | 2 +-
2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index e21dc71b1907..e064ded6fbec 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -565,7 +565,7 @@ static struct pci_bus *pci_alloc_bus(struct pci_bus *parent)
return b;
}

-static void devm_pci_release_host_bridge_dev(struct device *dev)
+static void pci_release_host_bridge_dev(struct device *dev)
{
struct pci_host_bridge *bridge = to_pci_host_bridge(dev);

@@ -574,12 +574,7 @@ static void devm_pci_release_host_bridge_dev(struct device *dev)

pci_free_resource_list(&bridge->windows);
pci_free_resource_list(&bridge->dma_ranges);
-}
-
-static void pci_release_host_bridge_dev(struct device *dev)
-{
- devm_pci_release_host_bridge_dev(dev);
- kfree(to_pci_host_bridge(dev));
+ kfree(bridge);
}

static void pci_init_host_bridge(struct pci_host_bridge *bridge)
@@ -599,6 +594,8 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge)
bridge->native_pme = 1;
bridge->native_ltr = 1;
bridge->native_dpc = 1;
+
+ device_initialize(&bridge->dev);
}

struct pci_host_bridge *pci_alloc_host_bridge(size_t priv)
@@ -616,17 +613,25 @@ struct pci_host_bridge *pci_alloc_host_bridge(size_t priv)
}
EXPORT_SYMBOL(pci_alloc_host_bridge);

+static void devm_pci_alloc_host_bridge_release(void *data)
+{
+ pci_free_host_bridge(data);
+}
+
struct pci_host_bridge *devm_pci_alloc_host_bridge(struct device *dev,
size_t priv)
{
+ int ret;
struct pci_host_bridge *bridge;

- bridge = devm_kzalloc(dev, sizeof(*bridge) + priv, GFP_KERNEL);
+ bridge = pci_alloc_host_bridge(priv);
if (!bridge)
return NULL;

- pci_init_host_bridge(bridge);
- bridge->dev.release = devm_pci_release_host_bridge_dev;
+ ret = devm_add_action_or_reset(dev, devm_pci_alloc_host_bridge_release,
+ bridge);
+ if (ret)
+ return NULL;

return bridge;
}
@@ -634,10 +639,7 @@ EXPORT_SYMBOL(devm_pci_alloc_host_bridge);

void pci_free_host_bridge(struct pci_host_bridge *bridge)
{
- pci_free_resource_list(&bridge->windows);
- pci_free_resource_list(&bridge->dma_ranges);
-
- kfree(bridge);
+ put_device(&bridge->dev);
}
EXPORT_SYMBOL(pci_free_host_bridge);

@@ -908,7 +910,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
if (err)
goto free;

- err = device_register(&bridge->dev);
+ err = device_add(&bridge->dev);
if (err) {
put_device(&bridge->dev);
goto free;
@@ -978,7 +980,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)

unregister:
put_device(&bridge->dev);
- device_unregister(&bridge->dev);
+ device_del(&bridge->dev);

free:
kfree(bus);
@@ -2953,7 +2955,7 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
return bridge->bus;

err_out:
- kfree(bridge);
+ put_device(&bridge->dev);
return NULL;
}
EXPORT_SYMBOL_GPL(pci_create_root_bus);
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index e9c6b120cf45..95dec03d9f2a 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -160,6 +160,6 @@ void pci_remove_root_bus(struct pci_bus *bus)
host_bridge->bus = NULL;

/* remove the host bridge */
- device_unregister(&host_bridge->dev);
+ device_del(&host_bridge->dev);
}
EXPORT_SYMBOL_GPL(pci_remove_root_bus);
--
2.20.1