[PATCH 4.4 10/20] target: Fix COMPARE_AND_WRITE ref leak for non GOOD status

From: Greg Kroah-Hartman
Date: Mon Feb 13 2017 - 08:05:21 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

commit 9b2792c3da1e80f2d460167d319302a24c9ca2b7 upstream.

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

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@xxxxxxxxx>
Cc: Donald White <dew@xxxxxxxxx>
Tested-by: Gary Guo <ghg@xxxxxxxxx>
Cc: Gary Guo <ghg@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/target/target_core_sbc.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -442,6 +442,7 @@ static sense_reason_t compare_and_write_
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
@@ -449,9 +450,12 @@ static sense_reason_t compare_and_write_
* sent to the backend driver.
- 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)

@@ -461,7 +465,7 @@ static sense_reason_t compare_and_write_

- return TCM_NO_SENSE;
+ return ret;

static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success,