scsi: target: Fix unmap setup during configuration

This issue was found and also debugged by Carl Lei <me@xecycle.info>.

If the device is not enabled, iblock/file will have not setup their
se_device to bdev/file mappings. If a user tries to config the unmap
settings at this time, we will then crash trying to access a NULL pointer
where the bdev/file should be.

This patch adds a check to make sure the device is configured before
we try to call the configure_unmap callout.

Fixes: 34bd1dca ("scsi: target: Detect UNMAP support post configuration")
Reported-by: Carl Lei <me@xecycle.info>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20240209215247.5213-1-michael.christie@oracle.comReviewed-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_configfs.c

@@ -759,6 +759,29 @@ static ssize_t emulate_tas_store(struct config_item *item,
 	return count;
 }
 
+static int target_try_configure_unmap(struct se_device *dev,
+				      const char *config_opt)
+{
+	if (!dev->transport->configure_unmap) {
+		pr_err("Generic Block Discard not supported\n");
+		return -ENOSYS;
+	}
+
+	if (!target_dev_configured(dev)) {
+		pr_err("Generic Block Discard setup for %s requires device to be configured\n",
+		       config_opt);
+		return -ENODEV;
+	}
+
+	if (!dev->transport->configure_unmap(dev)) {
+		pr_err("Generic Block Discard setup for %s failed\n",
+		       config_opt);
+		return -ENOSYS;
+	}
+
+	return 0;
+}
+
 static ssize_t emulate_tpu_store(struct config_item *item,
 		const char *page, size_t count)
 {
@@ -776,11 +799,9 @@ static ssize_t emulate_tpu_store(struct config_item *item,
 	 * Discard supported is detected iblock_create_virtdevice().
 	 */
 	if (flag && !da->max_unmap_block_desc_count) {
-		if (!dev->transport->configure_unmap ||
-		    !dev->transport->configure_unmap(dev)) {
-			pr_err("Generic Block Discard not supported\n");
-			return -ENOSYS;
-		}
+		ret = target_try_configure_unmap(dev, "emulate_tpu");
+		if (ret)
+			return ret;
 	}
 
 	da->emulate_tpu = flag;
@@ -806,11 +827,9 @@ static ssize_t emulate_tpws_store(struct config_item *item,
 	 * Discard supported is detected iblock_create_virtdevice().
 	 */
 	if (flag && !da->max_unmap_block_desc_count) {
-		if (!dev->transport->configure_unmap ||
-		    !dev->transport->configure_unmap(dev)) {
-			pr_err("Generic Block Discard not supported\n");
-			return -ENOSYS;
-		}
+		ret = target_try_configure_unmap(dev, "emulate_tpws");
+		if (ret)
+			return ret;
 	}
 
 	da->emulate_tpws = flag;
@@ -1022,12 +1041,9 @@ static ssize_t unmap_zeroes_data_store(struct config_item *item,
 	 * Discard supported is detected iblock_configure_device().
 	 */
 	if (flag && !da->max_unmap_block_desc_count) {
-		if (!dev->transport->configure_unmap ||
-		    !dev->transport->configure_unmap(dev)) {
-			pr_err("dev[%p]: Thin Provisioning LBPRZ will not be set because max_unmap_block_desc_count is zero\n",
-			       da->da_dev);
-			return -ENOSYS;
-		}
+		ret = target_try_configure_unmap(dev, "unmap_zeroes_data");
+		if (ret)
+			return ret;
 	}
 	da->unmap_zeroes_data = flag;
 	pr_debug("dev[%p]: SE Device Thin Provisioning LBPRZ bit: %d\n",