From: Rob Herring robh@kernel.org

commit 9885440b16b8fc1dd7275800fd28f56a92f60896 upstream.

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().

Link: https://lore.kernel.org/r/20200513223859.11295-2-robh@kernel.org Reported-by: Anders Roxell anders.roxell@linaro.org Tested-by: Anders Roxell anders.roxell@linaro.org Signed-off-by: Rob Herring robh@kernel.org Signed-off-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Lorenzo Pieralisi lorenzo.pieralisi@arm.com Acked-by: Arnd Bergmann arnd@arndb.de [tyhicks: Minor contextual change in pci_init_host_bridge() due to the lack of a native_dpc member in the pci_host_bridge struct. It was added in v5.7 with commit ac1c8e35a326 ("PCI/DPC: Add Error Disconnect Recover (EDR) support")] Signed-off-by: Tyler Hicks tyhicks@linux.microsoft.com ---

This commit has been identified as a fix for random memory corruption that we're experiencing in production. The memory corruption is easily reproducible on 5.4.150 and we get a nice KASAN splat that led us to discovering the upstream fix that wasn't marked for stable inclusion. I don't see any obvious reasons why this wouldn't be a valid linux-5.4.y candidate and hope we can get it applied there.

I've verified that the KASAN splat goes away and I don't see any other evidence of the memory corruption issue once this commit is applied to 5.4.150.

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 f28213b62527..a41d04c57642 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -564,7 +564,7 @@ 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);

@@ -573,12 +573,7 @@ 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) @@ -597,6 +592,8 @@ static void pci_init_host_bridge(struct pci_host_bridge *bridge) bridge->native_shpc_hotplug = 1; bridge->native_pme = 1; bridge->native_ltr = 1; + + device_initialize(&bridge->dev); }

struct pci_host_bridge *pci_alloc_host_bridge(size_t priv) @@ -614,17 +611,25 @@ 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; } @@ -632,10 +637,7 @@ 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);

@@ -866,7 +868,7 @@ 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; @@ -933,7 +935,7 @@ 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); @@ -2945,7 +2947,7 @@ 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);