Re: [PATCH V2] st: fix potential null pointer dereference.

[Tomas Henzl <thenzl@redhat.com>]

On 18.11.2015 15:32, 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] and STm->cdevs[rew] to NULL in
> case of failure.
>
> Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
> ---
>  drivers/scsi/st.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
> index e0a1e52..2e52295 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" : "",
> @@ -4110,8 +4110,9 @@ static int create_one_cdev(struct scsi_tape *tape, int mode, int rew)
>  	return 0;
>  out_free:
>  	cdev_del(STm->cdevs[rew]);
> -	STm->cdevs[rew] = NULL;
>  out:
> +	STm->cdevs[rew] = NULL;
> +	STm->devs[rew] = NULL;

Reviewed-by: Tomas Henzl <thenzl@redhat.com>