st: fix potential null pointer dereference.

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>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index b37b9b00c4b460ca97b44720d5aee1405c2d89ef..3e79c80bf6c6fbf009c83714187391ed25ed3dcb 100644 (file)
--- 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;
        return error;
 }