target: fix use-after-free with PSCSI sense data

The pointer to the sense buffer is fetched by transport_get_sense_data,
but this is called by target_complete_ok_work long after pscsi_req_done
has freed the struct that contains it.

Pass instead the fabric's sense buffer to transport_complete,
and copy the data to it directly in transport_complete.  Setting
SCF_TRANSPORT_TASK_SENSE also becomes a duty of transport_complete.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_pscsi.c

@@ -667,7 +667,8 @@ static void pscsi_free_device(void *p)
 	kfree(pdv);
 }
 
-static int pscsi_transport_complete(struct se_cmd *cmd, struct scatterlist *sg)
+static void pscsi_transport_complete(struct se_cmd *cmd, struct scatterlist *sg,
+				     unsigned char *sense_buffer)
 {
 	struct pscsi_dev_virt *pdv = cmd->se_dev->dev_ptr;
 	struct scsi_device *sd = pdv->pdv_sd;
@@ -679,7 +680,7 @@ static int pscsi_transport_complete(struct se_cmd *cmd, struct scatterlist *sg)
 	 * not been allocated because TCM is handling the emulation directly.
 	 */
 	if (!pt)
-		return 0;
+		return;
 
 	cdb = &pt->pscsi_cdb[0];
 	result = pt->pscsi_result;
@@ -750,10 +751,10 @@ after_mode_sense:
 	}
 after_mode_select:
 
-	if (status_byte(result) & CHECK_CONDITION)
-		return 1;
-
-	return 0;
+	if (sense_buffer && (status_byte(result) & CHECK_CONDITION)) {
+		memcpy(sense_buffer, pt->pscsi_sense, TRANSPORT_SENSE_BUFFER);
+		cmd->se_cmd_flags |= SCF_TRANSPORT_TASK_SENSE;
+	}
 }
 
 enum {
@@ -1184,13 +1185,6 @@ fail:
 	return -ENOMEM;
 }
 
-static unsigned char *pscsi_get_sense_buffer(struct se_cmd *cmd)
-{
-	struct pscsi_plugin_task *pt = cmd->priv;
-
-	return pt->pscsi_sense;
-}
-
 /*	pscsi_get_device_rev():
  *
  *
@@ -1273,7 +1267,6 @@ static struct se_subsystem_api pscsi_template = {
 	.check_configfs_dev_params = pscsi_check_configfs_dev_params,
 	.set_configfs_dev_params = pscsi_set_configfs_dev_params,
 	.show_configfs_dev_params = pscsi_show_configfs_dev_params,
-	.get_sense_buffer	= pscsi_get_sense_buffer,
 	.get_device_rev		= pscsi_get_device_rev,
 	.get_device_type	= pscsi_get_device_type,
 	.get_blocks		= pscsi_get_blocks,

drivers/target/target_core_transport.c

@@ -568,38 +568,31 @@ static void target_complete_failure_work(struct work_struct *work)
 }
 
 /*
- * Used to obtain Sense Data from underlying Linux/SCSI struct scsi_cmnd
+ * Used when asking transport to copy Sense Data from the underlying
+ * Linux/SCSI struct scsi_cmnd
  */
-static void transport_get_sense_data(struct se_cmd *cmd)
+static unsigned char *transport_get_sense_buffer(struct se_cmd *cmd)
 {
-	unsigned char *buffer = cmd->sense_buffer, *sense_buffer = NULL;
+	unsigned char *buffer = cmd->sense_buffer;
 	struct se_device *dev = cmd->se_dev;
-	unsigned long flags;
 	u32 offset = 0;
 
 	WARN_ON(!cmd->se_lun);
 
 	if (!dev)
-		return;
+		return NULL;
 
-	spin_lock_irqsave(&cmd->t_state_lock, flags);
-	if (cmd->se_cmd_flags & SCF_SENT_CHECK_CONDITION) {
-		spin_unlock_irqrestore(&cmd->t_state_lock, flags);
-		return;
-	}
-
-	sense_buffer = dev->transport->get_sense_buffer(cmd);
-	spin_unlock_irqrestore(&cmd->t_state_lock, flags);
+	if (cmd->se_cmd_flags & SCF_SENT_CHECK_CONDITION)
+		return NULL;
 
 	offset = cmd->se_tfo->set_fabric_sense_len(cmd, TRANSPORT_SENSE_BUFFER);
 
-	memcpy(&buffer[offset], sense_buffer, TRANSPORT_SENSE_BUFFER);
-
 	/* Automatically padded */
 	cmd->scsi_sense_length = TRANSPORT_SENSE_BUFFER + offset;
 
-	pr_debug("HBA_[%u]_PLUG[%s]: Set SAM STATUS: 0x%02x and sense\n",
+	pr_debug("HBA_[%u]_PLUG[%s]: Requesting sense for SAM STATUS: 0x%02x\n",
 		dev->se_hba->hba_id, dev->transport->name, cmd->scsi_status);
+	return &buffer[offset];
 }
 
 void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
@@ -615,12 +608,12 @@ void target_complete_cmd(struct se_cmd *cmd, u8 scsi_status)
 	cmd->transport_state &= ~CMD_T_BUSY;
 
 	if (dev && dev->transport->transport_complete) {
-		if (dev->transport->transport_complete(cmd,
-				cmd->t_data_sg) != 0) {
-			cmd->se_cmd_flags |= SCF_TRANSPORT_TASK_SENSE;
+		dev->transport->transport_complete(cmd,
+				cmd->t_data_sg,
+				transport_get_sense_buffer(cmd));
+		if (cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE)
 			success = 1;
 	}
-	}
 
 	/*
 	 * See if we are waiting to complete for an exception condition.
@@ -1987,12 +1980,11 @@ static void target_complete_ok_work(struct work_struct *work)
 		schedule_work(&cmd->se_dev->qf_work_queue);
 
 	/*
-	 * Check if we need to retrieve a sense buffer from
+	 * Check if we need to send a sense buffer from
 	 * the struct se_cmd in question.
 	 */
 	if (cmd->se_cmd_flags & SCF_TRANSPORT_TASK_SENSE) {
 		WARN_ON(!cmd->scsi_status);
-		transport_get_sense_data(cmd);
 		ret = transport_send_check_condition_and_sense(
 					cmd, 0, 1);
 		if (ret == -EAGAIN || ret == -ENOMEM)

include/target/target_core_backend.h

@@ -23,7 +23,9 @@ struct se_subsystem_api {
 	struct se_device *(*create_virtdevice)(struct se_hba *,
 				struct se_subsystem_dev *, void *);
 	void (*free_device)(void *);
-	int (*transport_complete)(struct se_cmd *cmd, struct scatterlist *);
+	void (*transport_complete)(struct se_cmd *cmd,
+				   struct scatterlist *,
+				   unsigned char *);
 
 	int (*parse_cdb)(struct se_cmd *cmd);
 	ssize_t (*check_configfs_dev_params)(struct se_hba *,