scsi: target: core: Prevent underflow for service actions

TCM buffer length doesn't necessarily equal 8 + ADDITIONAL LENGTH which
might be considered an underflow in case of Data-In size being greater than
8 + ADDITIONAL LENGTH. So truncate buffer length to prevent underflow.

Link: https://lore.kernel.org/r/20210209072202.41154-3-a.miloserdov@yadro.com
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>
Signed-off-by: Aleksandr Miloserdov <a.miloserdov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_pr.c

@@ -3739,6 +3739,7 @@ core_scsi3_pri_read_keys(struct se_cmd *cmd)
 	spin_unlock(&dev->t10_pr.registration_lock);
 
 	put_unaligned_be32(add_len, &buf[4]);
+	target_set_cmd_data_length(cmd, 8 + add_len);
 
 	transport_kunmap_data_sg(cmd);
 
@@ -3757,7 +3758,7 @@ core_scsi3_pri_read_reservation(struct se_cmd *cmd)
 	struct t10_pr_registration *pr_reg;
 	unsigned char *buf;
 	u64 pr_res_key;
-	u32 add_len = 16; /* Hardcoded to 16 when a reservation is held. */
+	u32 add_len = 0;
 
 	if (cmd->data_length < 8) {
 		pr_err("PRIN SA READ_RESERVATIONS SCSI Data Length: %u"
@@ -3775,8 +3776,9 @@ core_scsi3_pri_read_reservation(struct se_cmd *cmd)
 	pr_reg = dev->dev_pr_res_holder;
 	if (pr_reg) {
 		/*
-		 * Set the hardcoded Additional Length
+		 * Set the Additional Length to 16 when a reservation is held
 		 */
+		add_len = 16;
 		put_unaligned_be32(add_len, &buf[4]);
 
 		if (cmd->data_length < 22)
@@ -3812,6 +3814,8 @@ core_scsi3_pri_read_reservation(struct se_cmd *cmd)
 			  (pr_reg->pr_res_type & 0x0f);
 	}
 
+	target_set_cmd_data_length(cmd, 8 + add_len);
+
 err:
 	spin_unlock(&dev->dev_reservation_lock);
 	transport_kunmap_data_sg(cmd);
@@ -3830,7 +3834,7 @@ core_scsi3_pri_report_capabilities(struct se_cmd *cmd)
 	struct se_device *dev = cmd->se_dev;
 	struct t10_reservation *pr_tmpl = &dev->t10_pr;
 	unsigned char *buf;
-	u16 add_len = 8; /* Hardcoded to 8. */
+	u16 len = 8; /* Hardcoded to 8. */
 
 	if (cmd->data_length < 6) {
 		pr_err("PRIN SA REPORT_CAPABILITIES SCSI Data Length:"
@@ -3842,7 +3846,7 @@ core_scsi3_pri_report_capabilities(struct se_cmd *cmd)
 	if (!buf)
 		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 
-	put_unaligned_be16(add_len, &buf[0]);
+	put_unaligned_be16(len, &buf[0]);
 	buf[2] |= 0x10; /* CRH: Compatible Reservation Hanlding bit. */
 	buf[2] |= 0x08; /* SIP_C: Specify Initiator Ports Capable bit */
 	buf[2] |= 0x04; /* ATP_C: All Target Ports Capable bit */
@@ -3871,6 +3875,8 @@ core_scsi3_pri_report_capabilities(struct se_cmd *cmd)
 	buf[4] |= 0x02; /* PR_TYPE_WRITE_EXCLUSIVE */
 	buf[5] |= 0x01; /* PR_TYPE_EXCLUSIVE_ACCESS_ALLREG */
 
+	target_set_cmd_data_length(cmd, len);
+
 	transport_kunmap_data_sg(cmd);
 
 	return 0;
@@ -4031,6 +4037,7 @@ core_scsi3_pri_read_full_status(struct se_cmd *cmd)
 	 * Set ADDITIONAL_LENGTH
 	 */
 	put_unaligned_be32(add_len, &buf[4]);
+	target_set_cmd_data_length(cmd, 8 + add_len);
 
 	transport_kunmap_data_sg(cmd);