scsi: target: Fix NULL pointer dereference

NULL pointer dereference happens when the following conditions are met:

1) A SCSI command is received for a non-existing LU or cdb initialization
   fails in target_setup_cmd_from_cdb().

2) Tracing is enabled.

The following call sequences lead to NULL pointer dereference:

1) iscsit_setup_scsi_cmd
     transport_lookup_cmd_lun <-- lookup fails.
          or
     target_setup_cmd_from_cdb() <-- cdb initialization fails
   iscsit_process_scsi_cmd
     iscsit_sequence_cmd
       transport_send_check_condition_and_sense
         trace_target_cmd_complete <-- NULL dereference

2) target_submit_cmd_map_sgls
     transport_lookup_cmd_lun <-- lookup fails
          or
     target_setup_cmd_from_cdb() <-- cdb initialization fails
       transport_send_check_condition_and_sense
         trace_target_cmd_complete <-- NULL dereference

In the above sequence, cmd->t_task_cdb is uninitialized which when
referenced in trace_target_cmd_complete() causes NULL pointer dereference.

The fix is to use the helper, target_cmd_init_cdb() and call it after
transport_init_se_cmd() is called, so that cmd->t_task_cdb can be
initialized and hence can be referenced in trace_target_cmd_complete().

Link: https://lore.kernel.org/r/1591559913-8388-4-git-send-email-sudhakar.panneerselvam@oracle.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Sudhakar Panneerselvam <sudhakar.panneerselvam@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 25 insertions, 6 deletions

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 7ea77933e64d..0fbb38254535 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1413,6 +1413,9 @@ transport_check_alloc_task_attr(struct se_cmd *cmd)
 sense_reason_t
 target_cmd_init_cdb(struct se_cmd *cmd, unsigned char *cdb)
 {
+	sense_reason_t ret;
+
+	cmd->t_task_cdb = &cmd->__t_task_cdb[0];
 	/*
 	 * Ensure that the received CDB is less than the max (252 + 8) bytes
 	 * for VARIABLE_LENGTH_CMD
@@ -1421,7 +1424,8 @@ target_cmd_init_cdb(struct se_cmd *cmd, unsigned char *cdb)
 		pr_err("Received SCSI CDB with command_size: %d that"
 			" exceeds SCSI_MAX_VARLEN_CDB_SIZE: %d\n",
 			scsi_command_size(cdb), SCSI_MAX_VARLEN_CDB_SIZE);
-		return TCM_INVALID_CDB_FIELD;
+		ret = TCM_INVALID_CDB_FIELD;
+		goto err;
 	}
 	/*
 	 * If the received CDB is larger than TCM_MAX_COMMAND_SIZE,
@@ -1436,10 +1440,10 @@ target_cmd_init_cdb(struct se_cmd *cmd, unsigned char *cdb)
 				" %u > sizeof(cmd->__t_task_cdb): %lu ops\n",
 				scsi_command_size(cdb),
 				(unsigned long)sizeof(cmd->__t_task_cdb));
-			return TCM_OUT_OF_RESOURCES;
+			ret = TCM_OUT_OF_RESOURCES;
+			goto err;
 		}
-	} else
-		cmd->t_task_cdb = &cmd->__t_task_cdb[0];
+	}
 	/*
 	 * Copy the original CDB into cmd->
 	 */
@@ -1447,6 +1451,15 @@ target_cmd_init_cdb(struct se_cmd *cmd, unsigned char *cdb)
 
 	trace_target_sequencer_start(cmd);
 	return 0;
+
+err:
+	/*
+	 * Copy the CDB here to allow trace_target_cmd_complete() to
+	 * print the cdb to the trace buffers.
+	 */
+	memcpy(cmd->t_task_cdb, cdb, min(scsi_command_size(cdb),
+					 (unsigned int)TCM_MAX_COMMAND_SIZE));
+	return ret;
 }
 EXPORT_SYMBOL(target_cmd_init_cdb);
 
@@ -1456,8 +1469,6 @@ target_setup_cmd_from_cdb(struct se_cmd *cmd, unsigned char *cdb)
 	struct se_device *dev = cmd->se_dev;
 	sense_reason_t ret;
 
-	target_cmd_init_cdb(cmd, cdb);
-
 	ret = dev->transport->parse_cdb(cmd);
 	if (ret == TCM_UNSUPPORTED_SCSI_OPCODE)
 		pr_warn_ratelimited("%s/%s: Unsupported SCSI Opcode 0x%02x, sending CHECK_CONDITION.\n",
@@ -1621,6 +1632,14 @@ int target_submit_cmd_map_sgls(struct se_cmd *se_cmd, struct se_session *se_sess
 	 */
 	if (flags & TARGET_SCF_BIDI_OP)
 		se_cmd->se_cmd_flags |= SCF_BIDI;
+
+	rc = target_cmd_init_cdb(se_cmd, cdb);
+	if (rc) {
+		transport_send_check_condition_and_sense(se_cmd, rc, 0);
+		target_put_sess_cmd(se_cmd);
+		return 0;
+	}
+
 	/*
 	 * Locate se_lun pointer and attach it to struct se_cmd
 	 */