[PATCH 1/2] PCI: Fix pci_register_host_bridge() device_register() error handling

[PATCH 1/2] PCI: Fix pci_register_host_bridge() device_register() error handling

[Rob Herring]

If device_register() has an error, we should bail out of
pci_register_host_bridge() rather than continuing on.

Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rob Herring <robh@kernel.org>
---
 drivers/pci/probe.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 77b8a145c39b..e21dc71b1907 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -909,9 +909,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
 		goto free;
 
 	err = device_register(&bridge->dev);
-	if (err)
+	if (err) {
 		put_device(&bridge->dev);
-
+		goto free;
+	}
 	bus->bridge = get_device(&bridge->dev);
 	device_enable_async_suspend(bus->bridge);
 	pci_set_bus_of_node(bus);
-- 
2.20.1

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

[Rob Herring]

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

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

[Anders Roxell]

On Thu, 14 May 2020 at 00:39, Rob Herring <robh@kernel.org> wrote:
>
> 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>

Thank you Rob for fixing this so quickly!

I applied both patches and I couldn't see the use-after-free anymore.

Tested-by: Anders Roxell <anders.roxell@linaro.org>

Cheers,
Anders

> ---
>  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
>

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

[Lorenzo Pieralisi]

On Wed, May 13, 2020 at 05:38:59PM -0500, Rob Herring wrote:
> 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);

I think we need to execute device_del() first, then put_device().

Thank you for fixing this code path.

Lorenzo

>  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
> 

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

[Rob Herring]

On Thu, May 14, 2020 at 5:30 AM Lorenzo Pieralisi
<lorenzo.pieralisi@arm.com> wrote:
>
> On Wed, May 13, 2020 at 05:38:59PM -0500, Rob Herring wrote:
> > 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(-)

[...]

> > @@ -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);
>
> I think we need to execute device_del() first, then put_device().

No, because after the device_add, there's a get_device() adding the
bridge ptr to the bus. So the put_device here is for that. The final
put_device() is in the bridge free or devm action.

Rob

Re: [PATCH 1/2] PCI: Fix pci_register_host_bridge() device_register() error handling

[Lorenzo Pieralisi]

On Wed, May 13, 2020 at 05:38:58PM -0500, Rob Herring wrote:
> If device_register() has an error, we should bail out of
> pci_register_host_bridge() rather than continuing on.
> 
> Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---
>  drivers/pci/probe.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 77b8a145c39b..e21dc71b1907 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -909,9 +909,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  		goto free;
>  
>  	err = device_register(&bridge->dev);
> -	if (err)
> +	if (err) {
>  		put_device(&bridge->dev);
> -
> +		goto free;
> +	}
>  	bus->bridge = get_device(&bridge->dev);
>  	device_enable_async_suspend(bus->bridge);
>  	pci_set_bus_of_node(bus);
> -- 
> 2.20.1
> 

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

[Lorenzo Pieralisi]

On Wed, May 13, 2020 at 05:38:59PM -0500, Rob Herring wrote:
> 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(-)

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

> 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
> 

Re: [PATCH 1/2] PCI: Fix pci_register_host_bridge() device_register() error handling

[Arnd Bergmann]

On Thu, May 14, 2020 at 12:39 AM Rob Herring <robh@kernel.org> wrote:
>
> If device_register() has an error, we should bail out of
> pci_register_host_bridge() rather than continuing on.
>
> Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

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

[Arnd Bergmann]

On Thu, May 14, 2020 at 12:39 AM Rob Herring <robh@kernel.org> wrote:
>
> 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>

Thanks for working your way through that bit of code
and fixing my mistakes!

Your description makes a lot of sense and the code looks
reasonable, but I don't understand my own work enough any
more to be sure I didn't miss anything.

Acked-by: Arnd Bergmann <arnd@arndb.de>

Re: [PATCH 1/2] PCI: Fix pci_register_host_bridge() device_register() error handling

[Bjorn Helgaas]

On Wed, May 13, 2020 at 05:38:58PM -0500, Rob Herring wrote:
> If device_register() has an error, we should bail out of
> pci_register_host_bridge() rather than continuing on.
> 
> Fixes: 37d6a0a6f470 ("PCI: Add pci_register_host_bridge() interface")
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Rob Herring <robh@kernel.org>

Both applied to pci/enumeration for v5.8, thanks!

> ---
>  drivers/pci/probe.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 77b8a145c39b..e21dc71b1907 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -909,9 +909,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>  		goto free;
>  
>  	err = device_register(&bridge->dev);
> -	if (err)
> +	if (err) {
>  		put_device(&bridge->dev);
> -
> +		goto free;
> +	}
>  	bus->bridge = get_device(&bridge->dev);
>  	device_enable_async_suspend(bus->bridge);
>  	pci_set_bus_of_node(bus);
> -- 
> 2.20.1
>