linux-kernel - [PATCH 3.16 287/370] target: Fix COMPARE_AND

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Message-ID: <lsq.1489146383.456888232@decadent.org.uk>
Date:   Fri, 10 Mar 2017 11:46:23 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Donald White" <dew@...era.io>,
        "Nicholas Bellinger" <nab@...ux-iscsi.org>,
        "Christoph Hellwig" <hch@....de>, "Gary Guo" <ghg@...era.io>
Subject: [PATCH 3.16 287/370] target: Fix COMPARE_AND_WRITE ref leak for
 non GOOD status

3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Bellinger <nab@...ux-iscsi.org>

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
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@...era.io>
Cc: Donald White <dew@...era.io>
Tested-by: Gary Guo <ghg@...era.io>
Cc: Gary Guo <ghg@...era.io>
Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -368,6 +368,7 @@ 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
@@ -375,9 +376,12 @@ static sense_reason_t compare_and_write_
 	 * 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);

@@ -387,7 +391,7 @@ static sense_reason_t compare_and_write_
 	 */
 	up(&dev->caw_sem);

-	return TCM_NO_SENSE;
+	return ret;
 }

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