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>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index b37b9b00c4b4..3e79c80bf6c6 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;
         return error;
 }