vfio: ccw: set ccw->cda to NULL defensively

Let's avoid free on ccw->cda that points to a guest address
or an already freed memory area by setting it to NULL if memory
allocation didn't happen or failed.
Signed-off-by: NDong Jia Shi <bjsdjshi@linux.ibm.com>
Message-Id: <20180523025645.8978-4-bjsdjshi@linux.ibm.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>

drivers/s390/cio/vfio_ccw_cp.c

@@ -502,7 +502,7 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
 	struct ccw1 *ccw;
 	struct pfn_array_table *pat;
 	unsigned long *idaws;
-	int idaw_nr;
+	int ret;
 
 	ccw = chain->ch_ccw + idx;
 
@@ -522,18 +522,19 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
 	 * needed when translating a direct ccw to a idal ccw.
 	 */
 	pat = chain->ch_pat + idx;
-	if (pfn_array_table_init(pat, 1))
-		return -ENOMEM;
-	idaw_nr = pfn_array_alloc_pin(pat->pat_pa, cp->mdev,
-				      ccw->cda, ccw->count);
-	if (idaw_nr < 0)
-		return idaw_nr;
+	ret = pfn_array_table_init(pat, 1);
+	if (ret)
+		goto out_init;
+
+	ret = pfn_array_alloc_pin(pat->pat_pa, cp->mdev, ccw->cda, ccw->count);
+	if (ret < 0)
+		goto out_init;
 
 	/* Translate this direct ccw to a idal ccw. */
-	idaws = kcalloc(idaw_nr, sizeof(*idaws), GFP_DMA | GFP_KERNEL);
+	idaws = kcalloc(ret, sizeof(*idaws), GFP_DMA | GFP_KERNEL);
 	if (!idaws) {
-		pfn_array_table_unpin_free(pat, cp->mdev);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out_unpin;
 	}
 	ccw->cda = (__u32) virt_to_phys(idaws);
 	ccw->flags |= CCW_FLAG_IDA;
@@ -541,6 +542,12 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
 	pfn_array_table_idal_create_words(pat, idaws);
 
 	return 0;
+
+out_unpin:
+	pfn_array_table_unpin_free(pat, cp->mdev);
+out_init:
+	ccw->cda = 0;
+	return ret;
 }
 
 static int ccwchain_fetch_idal(struct ccwchain *chain,
@@ -570,7 +577,7 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
 	pat = chain->ch_pat + idx;
 	ret = pfn_array_table_init(pat, idaw_nr);
 	if (ret)
-		return ret;
+		goto out_init;
 
 	/* Translate idal ccw to use new allocated idaws. */
 	idaws = kzalloc(idaw_len, GFP_DMA | GFP_KERNEL);
@@ -602,6 +609,8 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
 	kfree(idaws);
 out_unpin:
 	pfn_array_table_unpin_free(pat, cp->mdev);
+out_init:
+	ccw->cda = 0;
 	return ret;
 }