scsi: target: Fix WRITE_SAME No Data Buffer crash

In newer version of the SBC specs, we have a NDOB bit that indicates there
is no data buffer that gets written out. If this bit is set using commands
like "sg_write_same --ndob" we will crash in target_core_iblock/file's
execute_write_same handlers when we go to access the se_cmd->t_data_sg
because its NULL.

This patch adds a check for the NDOB bit in the common WRITE SAME code
because we don't support it. And, it adds a check for zero SG elements in
each handler in case the initiator tries to send a normal WRITE SAME with
no data buffer.

Link: https://lore.kernel.org/r/20220628022325.14627-2-michael.christie@oracle.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_file.c

@@ -448,6 +448,9 @@ fd_execute_write_same(struct se_cmd *cmd)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 	}
 
+	if (!cmd->t_data_nents)
+		return TCM_INVALID_CDB_FIELD;
+
 	if (cmd->t_data_nents > 1 ||
 	    cmd->t_data_sg[0].length != cmd->se_dev->dev_attrib.block_size) {
 		pr_err("WRITE_SAME: Illegal SGL t_data_nents: %u length: %u"

drivers/target/target_core_iblock.c

@@ -494,6 +494,10 @@ iblock_execute_write_same(struct se_cmd *cmd)
 		       " backends not supported\n");
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 	}
+
+	if (!cmd->t_data_nents)
+		return TCM_INVALID_CDB_FIELD;
+
 	sg = &cmd->t_data_sg[0];
 
 	if (cmd->t_data_nents > 1 ||

drivers/target/target_core_sbc.c

@@ -312,6 +312,12 @@ sbc_setup_write_same(struct se_cmd *cmd, unsigned char flags, struct sbc_ops *op
 		pr_warn("WRITE SAME with ANCHOR not supported\n");
 		return TCM_INVALID_CDB_FIELD;
 	}
+
+	if (flags & 0x01) {
+		pr_warn("WRITE SAME with NDOB not supported\n");
+		return TCM_INVALID_CDB_FIELD;
+	}
+
 	/*
 	 * Special case for WRITE_SAME w/ UNMAP=1 that ends up getting
 	 * translated into block discard requests within backend code.