[PATCH v2 1/1] firmware_loader: Fix use-after-free during unregister

[Russ Weight]

In the following code within firmware_upload_unregister(), the call to
device_unregister() could result in the dev_release function freeing the
fw_upload_priv structure before it is dereferenced for the call to
module_put(). This bug was found by the kernel test robot using
CONFIG_KASAN while running the firmware selftests.

  device_unregister(&fw_sysfs->dev);
  module_put(fw_upload_priv->module);

The problem is fixed by copying fw_upload_priv->module to a local variable
for use when calling device_unregister().

Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Fixes: 97730bbb242c ("firmware_loader: Add firmware-upload support")
Signed-off-by: Russ Weight <russell.h.weight@xxxxxxxxx>
---
v2: Rebased to latest linux-next branch (next-20220829)
---
 drivers/base/firmware_loader/sysfs_upload.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/base/firmware_loader/sysfs_upload.c b/drivers/base/firmware_loader/sysfs_upload.c
index 87044d52322a..63e15bddd80c 100644
--- a/drivers/base/firmware_loader/sysfs_upload.c
+++ b/drivers/base/firmware_loader/sysfs_upload.c
@@ -377,6 +377,7 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
 {
 	struct fw_sysfs *fw_sysfs = fw_upload->priv;
 	struct fw_upload_priv *fw_upload_priv = fw_sysfs->fw_upload_priv;
+	struct module *module = fw_upload_priv->module;
 
 	mutex_lock(&fw_upload_priv->lock);
 	if (fw_upload_priv->progress == FW_UPLOAD_PROG_IDLE) {
@@ -392,6 +393,6 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
 
 unregister:
 	device_unregister(&fw_sysfs->dev);
-	module_put(fw_upload_priv->module);
+	module_put(module);
 }
 EXPORT_SYMBOL_GPL(firmware_upload_unregister);
-- 
2.25.1