target: Fix COMPARE_AND_WRITE ref leak for non GOOD status

This patch addresses a long standing bug where the commit phase
of COMPARE_AND_WRITE would result in a se_cmd->cmd_kref reference
leak if se_cmd->scsi_status returned non SAM_STAT_GOOD.

This would manifest first as a lost SCSI response, and eventual
hung task during fabric driver logout or re-login, as existing
shutdown logic waited for the COMPARE_AND_WRITE se_cmd->cmd_kref
to reach zero.

To address this bug, compare_and_write_post() has been changed
to drop the incorrect !cmd->scsi_status conditional that was
preventing *post_ret = 1 for being set during non SAM_STAT_GOOD
status.

This patch has been tested with SAM_STAT_CHECK_CONDITION status
from normal target_complete_cmd() callback path, as well as the
incoming __target_execute_cmd() submission failure path when
se_cmd->execute_cmd() returns non zero status.

Reported-by: Donald White <dew@datera.io>
Cc: Donald White <dew@datera.io>
Tested-by: Gary Guo <ghg@datera.io>
Cc: Gary Guo <ghg@datera.io>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: <stable@vger.kernel.org> # v3.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 4879e70e2eef..df7b6e95c019 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -451,6 +451,7 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,
                                              int *post_ret)
 {
         struct se_device *dev = cmd->se_dev;
+        sense_reason_t ret = TCM_NO_SENSE;
 
         /*
          * Only set SCF_COMPARE_AND_WRITE_POST to force a response fall-through
@@ -458,9 +459,12 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,
          * sent to the backend driver.
          */
         spin_lock_irq(&cmd->t_state_lock);
-        if ((cmd->transport_state & CMD_T_SENT) && !cmd->scsi_status) {
+        if (cmd->transport_state & CMD_T_SENT) {
                 cmd->se_cmd_flags |= SCF_COMPARE_AND_WRITE_POST;
                 *post_ret = 1;
+
+                if (cmd->scsi_status == SAM_STAT_CHECK_CONDITION)
+                        ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
         }
         spin_unlock_irq(&cmd->t_state_lock);
 
@@ -470,7 +474,7 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,
          */
         up(&dev->caw_sem);
 
-        return TCM_NO_SENSE;
+        return ret;
 }
 
 static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success,