[PATCH 1/2] tpm/tpm_ibmvtpm: Fail in ibmvtpm_get_data if driver_data is bad

[Anton Blanchard <anton@samba.org>]

I'm looking at an oops in tpm_ibmvtpm_get_desired_dma:

  28:	00 00 20 39 	li      r9,0
  2c:	10 00 01 e8 	ld      r0,16(r1)
  30:	28 00 69 80 	lwz     r3,40(r9)

We set r9 to 0 then load r9+40. The problem is actually in
ibmvtpm_get_data, it can return NULL but the rest of the driver
never expects it.

Add a BUG_ON in ibmvtpm_get_data. We still need to identify the root
cause but at least this makes it obvious what went wrong.

Cc: stable@vger.kernel.org
Signed-off-by: Anton Blanchard <anton@samba.org>
---

diff --git a/drivers/char/tpm/tpm_ibmvtpm.c b/drivers/char/tpm/tpm_ibmvtpm.c
index af74c57..0d1eeba 100644
--- a/drivers/char/tpm/tpm_ibmvtpm.c
+++ b/drivers/char/tpm/tpm_ibmvtpm.c
@@ -63,9 +63,9 @@ static int ibmvtpm_send_crq(struct vio_dev *vdev, u64 w1, u64 w2)
 static struct ibmvtpm_dev *ibmvtpm_get_data(const struct device *dev)
 {
 	struct tpm_chip *chip = dev_get_drvdata(dev);
-	if (chip)
-		return (struct ibmvtpm_dev *)TPM_VPRIV(chip);
-	return NULL;
+
+	BUG_ON(!chip);
+	return (struct ibmvtpm_dev *)TPM_VPRIV(chip);
 }
 
 /**