[PATCH] st: fix potential null pointer dereference.

[PATCH] st: fix potential null pointer dereference.

[Maurizio Lombardi]

If cdev_add() returns an error, the code calls
cdev_del() passing the STm->cdevs[rew] pointer as parameter;
the problem is that the pointer has not been initialized yet.

This patch fixes the problem by moving the STm->cdevs[rew] pointer
initialization before the call to cdev_add().
It also sets STm->devs[rew] = NULL if device_create() fails, just to be
sure we won't end up calling device_unregister() with an invalid pointer.

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
---
 drivers/scsi/st.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index e0a1e52..dff3bdb 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4083,6 +4083,7 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
 	}
 	cdev->owner = THIS_MODULE;
 	cdev->ops = &st_fops;
+	STm->cdevs[rew] = cdev;
 
 	error = cdev_add(cdev, cdev_devno, 1);
 	if (error) {
@@ -4091,7 +4092,6 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
 		pr_err("st%d: Device not attached.\n", dev_num);
 		goto out_free;
 	}
-	STm->cdevs[rew] = cdev;
 
 	i = mode << (4 - ST_NBR_MODE_BITS);
 	snprintf(name, 10, "%s%s%s", rew ? "n" : "",
@@ -4102,6 +4102,7 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
 	if (IS_ERR(dev)) {
 		pr_err("st%d: device_create failed\n", dev_num);
 		error = PTR_ERR(dev);
+		STm->devs[rew] = NULL;
 		goto out_free;
 	}
 
-- 
Maurizio Lombardi

Re: [PATCH] st: fix potential null pointer dereference.

[Maurizio Lombardi]

Please ignore this one, I sent a V2

On 11/18/2015 02:18 PM, Maurizio Lombardi wrote:
> If cdev_add() returns an error, the code calls
> cdev_del() passing the STm->cdevs[rew] pointer as parameter;
> the problem is that the pointer has not been initialized yet.
> 
> This patch fixes the problem by moving the STm->cdevs[rew] pointer
> initialization before the call to cdev_add().
> It also sets STm->devs[rew] = NULL if device_create() fails, just to be
> sure we won't end up calling device_unregister() with an invalid pointer.
> 
> Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
> ---
>  drivers/scsi/st.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
> index e0a1e52..dff3bdb 100644
> --- a/drivers/scsi/st.c
> +++ b/drivers/scsi/st.c
> @@ -4083,6 +4083,7 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
>  	}
>  	cdev->owner = THIS_MODULE;
>  	cdev->ops = &st_fops;
> +	STm->cdevs[rew] = cdev;
>  
>  	error = cdev_add(cdev, cdev_devno, 1);
>  	if (error) {
> @@ -4091,7 +4092,6 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
>  		pr_err("st%d: Device not attached.\n", dev_num);
>  		goto out_free;
>  	}
> -	STm->cdevs[rew] = cdev;
>  
>  	i = mode << (4 - ST_NBR_MODE_BITS);
>  	snprintf(name, 10, "%s%s%s", rew ? "n" : "",
> @@ -4102,6 +4102,7 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
>  	if (IS_ERR(dev)) {
>  		pr_err("st%d: device_create failed\n", dev_num);
>  		error = PTR_ERR(dev);
> +		STm->devs[rew] = NULL;
>  		goto out_free;
>  	}
>  
>