iscsi-target: Fix TMR reference leak during session shutdown

This patch fixes a iscsi-target specific TMR reference leak
during session shutdown, that could occur when a TMR was
quiesced before the hand-off back to iscsi-target code
via transport_cmd_check_stop_to_fabric().

The reference leak happens because iscsit_free_cmd() was
incorrectly skipping the final target_put_sess_cmd() for
TMRs when transport_generic_free_cmd() returned zero because
the se_cmd->cmd_kref did not reach zero, due to the missing
se_cmd assignment in original code.

The result was iscsi_cmd and it's associated se_cmd memory
would be freed once se_sess->sess_cmd_map where released,
but the associated se_tmr_req was leaked and remained part
of se_device->dev_tmr_list.

This bug would manfiest itself as kernel paging request
OOPsen in core_tmr_lun_reset(), when a left-over se_tmr_req
attempted to dereference it's se_cmd pointer that had
already been released during normal session shutdown.

To address this bug, go ahead and treat ISCSI_OP_SCSI_CMD
and ISCSI_OP_SCSI_TMFUNC the same when there is an extra
se_cmd->cmd_kref to drop in iscsit_free_cmd(), and use
op_scsi to signal __iscsit_free_cmd() when the former
needs to clear any further iscsi related I/O state.

Reported-by: Rob Millner <rlm@daterainc.com>
Cc: Rob Millner <rlm@daterainc.com>
Reported-by: Chu Yuan Lin <cyl@datera.io>
Cc: Chu Yuan Lin <cyl@datera.io>
Tested-by: Chu Yuan Lin <cyl@datera.io>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 5041a9c8bdcb..b4640338f8d8 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -737,21 +737,23 @@ void iscsit_free_cmd(struct iscsi_cmd *cmd, bool shutdown)
 {
         struct se_cmd *se_cmd = NULL;
         int rc;
+        bool op_scsi = false;
         /*
          * Determine if a struct se_cmd is associated with
          * this struct iscsi_cmd.
          */
         switch (cmd->iscsi_opcode) {
         case ISCSI_OP_SCSI_CMD:
-                se_cmd = &cmd->se_cmd;
-                __iscsit_free_cmd(cmd, true, shutdown);
+                op_scsi = true;
                 /*
                  * Fallthrough
                  */
         case ISCSI_OP_SCSI_TMFUNC:
-                rc = transport_generic_free_cmd(&cmd->se_cmd, shutdown);
-                if (!rc && shutdown && se_cmd && se_cmd->se_sess) {
-                        __iscsit_free_cmd(cmd, true, shutdown);
+                se_cmd = &cmd->se_cmd;
+                __iscsit_free_cmd(cmd, op_scsi, shutdown);
+                rc = transport_generic_free_cmd(se_cmd, shutdown);
+                if (!rc && shutdown && se_cmd->se_sess) {
+                        __iscsit_free_cmd(cmd, op_scsi, shutdown);
                         target_put_sess_cmd(se_cmd);
                 }
                 break;