The current implementation of the fpga bridge assumes that the low-level
module registers a driver for the parent device and uses its owner pointer
to take the module's refcount. This approach is problematic since it can
lead to a null pointer dereference while attempting to get the bridge if
the parent device does not have a driver.
To address this problem, add a module owner pointer to the fpga_bridge
struct and use it to take the module's refcount. Modify the function for
registering a bridge to take an additional owner module parameter and
rename it to avoid conflicts. Use the old function name for a helper macro
that automatically sets the module that registers the bridge as the owner.
This ensures compatibility with existing low-level control modules and
reduces the chances of registering a bridge without setting the owner.
Also, update the documentation to keep it consistent with the new interface
for registering an fpga bridge.
Other changes: opportunistically move put_device() from __fpga_bridge_get()
to fpga_bridge_get() and of_fpga_bridge_get() to improve code clarity since
the bridge device is taken in these functions.
Fixes: 21aeda950c5f ("fpga: add fpga bridge framework")
Suggested-by: Greg Kroah-Hartman <[email protected]>
Suggested-by: Xu Yilun <[email protected]>
Reviewed-by: Russ Weight <[email protected]>
Signed-off-by: Marco Pagani <[email protected]>
---
v3:
- Add reviewed-by Russ Weight
- Fix typo in the documentation (bridge -> FPGA bridge)
v2:
- Split out protection against races while taking the mod's refcount
---
Documentation/driver-api/fpga/fpga-bridge.rst | 7 ++-
drivers/fpga/fpga-bridge.c | 57 ++++++++++---------
include/linux/fpga/fpga-bridge.h | 10 +++-
3 files changed, 43 insertions(+), 31 deletions(-)
diff --git a/Documentation/driver-api/fpga/fpga-bridge.rst b/Documentation/driver-api/fpga/fpga-bridge.rst
index 604208534095..833f68fb0700 100644
--- a/Documentation/driver-api/fpga/fpga-bridge.rst
+++ b/Documentation/driver-api/fpga/fpga-bridge.rst
@@ -6,9 +6,12 @@ API to implement a new FPGA bridge
* struct fpga_bridge - The FPGA Bridge structure
* struct fpga_bridge_ops - Low level Bridge driver ops
-* fpga_bridge_register() - Create and register a bridge
+* __fpga_bridge_register() - Create and register a bridge
* fpga_bridge_unregister() - Unregister a bridge
+The helper macro ``fpga_bridge_register()`` automatically sets
+the module that registers the FPGA bridge as the owner.
+
.. kernel-doc:: include/linux/fpga/fpga-bridge.h
:functions: fpga_bridge
@@ -16,7 +19,7 @@ API to implement a new FPGA bridge
:functions: fpga_bridge_ops
.. kernel-doc:: drivers/fpga/fpga-bridge.c
- :functions: fpga_bridge_register
+ :functions: __fpga_bridge_register
.. kernel-doc:: drivers/fpga/fpga-bridge.c
:functions: fpga_bridge_unregister
diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
index 79c473b3c7c3..8ef395b49bf8 100644
--- a/drivers/fpga/fpga-bridge.c
+++ b/drivers/fpga/fpga-bridge.c
@@ -55,33 +55,26 @@ int fpga_bridge_disable(struct fpga_bridge *bridge)
}
EXPORT_SYMBOL_GPL(fpga_bridge_disable);
-static struct fpga_bridge *__fpga_bridge_get(struct device *dev,
+static struct fpga_bridge *__fpga_bridge_get(struct device *bridge_dev,
struct fpga_image_info *info)
{
struct fpga_bridge *bridge;
- int ret = -ENODEV;
- bridge = to_fpga_bridge(dev);
+ bridge = to_fpga_bridge(bridge_dev);
bridge->info = info;
- if (!mutex_trylock(&bridge->mutex)) {
- ret = -EBUSY;
- goto err_dev;
- }
+ if (!mutex_trylock(&bridge->mutex))
+ return ERR_PTR(-EBUSY);
- if (!try_module_get(dev->parent->driver->owner))
- goto err_ll_mod;
+ if (!try_module_get(bridge->br_ops_owner)) {
+ mutex_unlock(&bridge->mutex);
+ return ERR_PTR(-ENODEV);
+ }
dev_dbg(&bridge->dev, "get\n");
return bridge;
-
-err_ll_mod:
- mutex_unlock(&bridge->mutex);
-err_dev:
- put_device(dev);
- return ERR_PTR(ret);
}
/**
@@ -98,13 +91,18 @@ static struct fpga_bridge *__fpga_bridge_get(struct device *dev,
struct fpga_bridge *of_fpga_bridge_get(struct device_node *np,
struct fpga_image_info *info)
{
- struct device *dev;
+ struct fpga_bridge *bridge;
+ struct device *bridge_dev;
- dev = class_find_device_by_of_node(&fpga_bridge_class, np);
- if (!dev)
+ bridge_dev = class_find_device_by_of_node(&fpga_bridge_class, np);
+ if (!bridge_dev)
return ERR_PTR(-ENODEV);
- return __fpga_bridge_get(dev, info);
+ bridge = __fpga_bridge_get(bridge_dev, info);
+ if (IS_ERR(bridge))
+ put_device(bridge_dev);
+
+ return bridge;
}
EXPORT_SYMBOL_GPL(of_fpga_bridge_get);
@@ -125,6 +123,7 @@ static int fpga_bridge_dev_match(struct device *dev, const void *data)
struct fpga_bridge *fpga_bridge_get(struct device *dev,
struct fpga_image_info *info)
{
+ struct fpga_bridge *bridge;
struct device *bridge_dev;
bridge_dev = class_find_device(&fpga_bridge_class, NULL, dev,
@@ -132,7 +131,11 @@ struct fpga_bridge *fpga_bridge_get(struct device *dev,
if (!bridge_dev)
return ERR_PTR(-ENODEV);
- return __fpga_bridge_get(bridge_dev, info);
+ bridge = __fpga_bridge_get(bridge_dev, info);
+ if (IS_ERR(bridge))
+ put_device(bridge_dev);
+
+ return bridge;
}
EXPORT_SYMBOL_GPL(fpga_bridge_get);
@@ -146,7 +149,7 @@ void fpga_bridge_put(struct fpga_bridge *bridge)
dev_dbg(&bridge->dev, "put\n");
bridge->info = NULL;
- module_put(bridge->dev.parent->driver->owner);
+ module_put(bridge->br_ops_owner);
mutex_unlock(&bridge->mutex);
put_device(&bridge->dev);
}
@@ -316,18 +319,19 @@ static struct attribute *fpga_bridge_attrs[] = {
ATTRIBUTE_GROUPS(fpga_bridge);
/**
- * fpga_bridge_register - create and register an FPGA Bridge device
+ * __fpga_bridge_register - create and register an FPGA Bridge device
* @parent: FPGA bridge device from pdev
* @name: FPGA bridge name
* @br_ops: pointer to structure of fpga bridge ops
* @priv: FPGA bridge private data
+ * @owner: owner module containing the br_ops
*
* Return: struct fpga_bridge pointer or ERR_PTR()
*/
struct fpga_bridge *
-fpga_bridge_register(struct device *parent, const char *name,
- const struct fpga_bridge_ops *br_ops,
- void *priv)
+__fpga_bridge_register(struct device *parent, const char *name,
+ const struct fpga_bridge_ops *br_ops,
+ void *priv, struct module *owner)
{
struct fpga_bridge *bridge;
int id, ret;
@@ -357,6 +361,7 @@ fpga_bridge_register(struct device *parent, const char *name,
bridge->name = name;
bridge->br_ops = br_ops;
+ bridge->br_ops_owner = owner;
bridge->priv = priv;
bridge->dev.groups = br_ops->groups;
@@ -386,7 +391,7 @@ fpga_bridge_register(struct device *parent, const char *name,
return ERR_PTR(ret);
}
-EXPORT_SYMBOL_GPL(fpga_bridge_register);
+EXPORT_SYMBOL_GPL(__fpga_bridge_register);
/**
* fpga_bridge_unregister - unregister an FPGA bridge
diff --git a/include/linux/fpga/fpga-bridge.h b/include/linux/fpga/fpga-bridge.h
index 223da48a6d18..94c4edd047e5 100644
--- a/include/linux/fpga/fpga-bridge.h
+++ b/include/linux/fpga/fpga-bridge.h
@@ -45,6 +45,7 @@ struct fpga_bridge_info {
* @dev: FPGA bridge device
* @mutex: enforces exclusive reference to bridge
* @br_ops: pointer to struct of FPGA bridge ops
+ * @br_ops_owner: module containing the br_ops
* @info: fpga image specific information
* @node: FPGA bridge list node
* @priv: low level driver private date
@@ -54,6 +55,7 @@ struct fpga_bridge {
struct device dev;
struct mutex mutex; /* for exclusive reference to bridge */
const struct fpga_bridge_ops *br_ops;
+ struct module *br_ops_owner;
struct fpga_image_info *info;
struct list_head node;
void *priv;
@@ -79,10 +81,12 @@ int of_fpga_bridge_get_to_list(struct device_node *np,
struct fpga_image_info *info,
struct list_head *bridge_list);
+#define fpga_bridge_register(parent, name, br_ops, priv) \
+ __fpga_bridge_register(parent, name, br_ops, priv, THIS_MODULE)
struct fpga_bridge *
-fpga_bridge_register(struct device *parent, const char *name,
- const struct fpga_bridge_ops *br_ops,
- void *priv);
+__fpga_bridge_register(struct device *parent, const char *name,
+ const struct fpga_bridge_ops *br_ops, void *priv,
+ struct module *owner);
void fpga_bridge_unregister(struct fpga_bridge *br);
#endif /* _LINUX_FPGA_BRIDGE_H */
base-commit: b1a91ca25f15b6d7b311de4465854a5981dee3d3
--
2.44.0
On Fri, Mar 22, 2024 at 06:18:37PM +0100, Marco Pagani wrote:
> The current implementation of the fpga bridge assumes that the low-level
> module registers a driver for the parent device and uses its owner pointer
> to take the module's refcount. This approach is problematic since it can
> lead to a null pointer dereference while attempting to get the bridge if
> the parent device does not have a driver.
>
> To address this problem, add a module owner pointer to the fpga_bridge
> struct and use it to take the module's refcount. Modify the function for
> registering a bridge to take an additional owner module parameter and
> rename it to avoid conflicts. Use the old function name for a helper macro
> that automatically sets the module that registers the bridge as the owner.
> This ensures compatibility with existing low-level control modules and
> reduces the chances of registering a bridge without setting the owner.
>
> Also, update the documentation to keep it consistent with the new interface
> for registering an fpga bridge.
>
> Other changes: opportunistically move put_device() from __fpga_bridge_get()
> to fpga_bridge_get() and of_fpga_bridge_get() to improve code clarity since
> the bridge device is taken in these functions.
>
> Fixes: 21aeda950c5f ("fpga: add fpga bridge framework")
> Suggested-by: Greg Kroah-Hartman <[email protected]>
> Suggested-by: Xu Yilun <[email protected]>
> Reviewed-by: Russ Weight <[email protected]>
> Signed-off-by: Marco Pagani <[email protected]>
Acked-by: Xu Yilun <[email protected]>
Applied to for-next.