linux-kernel - Re: [PATCH -next] scsi: core: fix double free in raid_component

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Date:   Mon, 21 Aug 2023 12:50:57 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Zhu Wang <wangzhu9@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, dan.carpenter@...aro.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] scsi: core: fix double free in raid_component_add()

On 8/19/23 01:03, Zhu Wang wrote:
> Previous commit 04b5b5cb0136 ("scsi: core: Fix possible memory leak if
> device_add() fails") introduced a double free when device_add() failed.
> When device_add() failed, the put_device(&rc->dev) is called, which will
> call raid_component_release(), and this function will call
> put_device(rc->dev.parent) and kfree(rc), but in the error path of
> raid_component_release() above two functions are called again, so 'rc' are
> freed twice.
> 
> We do not just revert the patch, since the memory allocated by
> dev_set_name() is not released in the error path, it should be released
> through calling put_device(&rc->dev) which will call kobject_cleanup(),
> and the device name will be released in it. Though the commit 04b5b5cb0136
> ("scsi: core: Fix possible memory leak if device_add() fails") fixed the
> memory leak, it didn't consider the double free problem. We removed
> put_device(rc->dev.parent) and kfree(rc) in the error path, and we moved
> put_device(&rc->dev) after rd->component-count--, since after
> put_device(&rc->dev) is called, 'rc' is freed, so list_del(&rc->node)
> cannot be called again.
> 
> Fixes: 04b5b5cb0136 ("scsi: core: Fix possible memory leak if device_add() fails")
> Signed-off-by: Zhu Wang <wangzhu9@...wei.com>
> ---
>   drivers/scsi/raid_class.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/raid_class.c b/drivers/scsi/raid_class.c
> index 711252e52d8e..86ed1f66d749 100644
> --- a/drivers/scsi/raid_class.c
> +++ b/drivers/scsi/raid_class.c
> @@ -248,11 +248,9 @@ int raid_component_add(struct raid_template *r,struct device *raid_dev,
>   	return 0;
>   
>   err_out:
> -	put_device(&rc->dev);
>   	list_del(&rc->node);
>   	rd->component_count--;
> -	put_device(component_dev);
> -	kfree(rc);
> +	put_device(&rc->dev);
>   	return err;
>   }
>   EXPORT_SYMBOL(raid_component_add);

Please consider replacing the above patch by the patch below:

[PATCH] scsi: Remove raid_component_add()

The raid_component_add() function was added to the kernel tree via
patch "[SCSI] embryonic RAID class" (2005). Remove this function since
it never has had any callers in the Linux kernel.

Signed-off-by: Bart Van Assche <bvanassche@....org>
---
  drivers/scsi/raid_class.c  | 38 --------------------------------------
  include/linux/raid_class.h |  4 ----
  2 files changed, 42 deletions(-)

diff --git a/drivers/scsi/raid_class.c b/drivers/scsi/raid_class.c
index 898a0bdf8df6..99f806d1d317 100644
--- a/drivers/scsi/raid_class.c
+++ b/drivers/scsi/raid_class.c
@@ -218,44 +218,6 @@ static void raid_component_release(struct device *dev)
  	kfree(rc);
  }

-int raid_component_add(struct raid_template *r,struct device *raid_dev,
-		       struct device *component_dev)
-{
-	struct device *cdev =
-		attribute_container_find_class_device(&r->raid_attrs.ac,
-						      raid_dev);
-	struct raid_component *rc;
-	struct raid_data *rd = dev_get_drvdata(cdev);
-	int err;
-
-	rc = kzalloc(sizeof(*rc), GFP_KERNEL);
-	if (!rc)
-		return -ENOMEM;
-
-	INIT_LIST_HEAD(&rc->node);
-	device_initialize(&rc->dev);
-	rc->dev.release = raid_component_release;
-	rc->dev.parent = get_device(component_dev);
-	rc->num = rd->component_count++;
-
-	dev_set_name(&rc->dev, "component-%d", rc->num);
-	list_add_tail(&rc->node, &rd->component_list);
-	rc->dev.class = &raid_class.class;
-	err = device_add(&rc->dev);
-	if (err)
-		goto err_out;
-
-	return 0;
-
-err_out:
-	list_del(&rc->node);
-	rd->component_count--;
-	put_device(component_dev);
-	kfree(rc);
-	return err;
-}
-EXPORT_SYMBOL(raid_component_add);
-
  struct raid_template *
  raid_class_attach(struct raid_function_template *ft)
  {
diff --git a/include/linux/raid_class.h b/include/linux/raid_class.h
index 6a9b177d5c41..e50416ba9cd9 100644
--- a/include/linux/raid_class.h
+++ b/include/linux/raid_class.h
@@ -77,7 +77,3 @@ DEFINE_RAID_ATTRIBUTE(enum raid_state, state)
  	
  struct raid_template *raid_class_attach(struct raid_function_template *);
  void raid_class_release(struct raid_template *);
-
-int __must_check raid_component_add(struct raid_template *, struct device *,
-				    struct device *);
-