[PATCH 3.10 232/268] iscsi-target: Fix TMR reference leak during session shutdown

From: Willy Tarreau
Date: Mon Jun 19 2017 - 15:16:01 EST

From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

commit efb2ea770bb3b0f40007530bc8b0c22f36e1c5eb upstream.

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@xxxxxxxxxxxxx>
Cc: Rob Millner <rlm@xxxxxxxxxxxxx>
Reported-by: Chu Yuan Lin <cyl@xxxxxxxxx>
Cc: Chu Yuan Lin <cyl@xxxxxxxxx>
Tested-by: Chu Yuan Lin <cyl@xxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
drivers/target/iscsi/iscsi_target_util.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target_util.c b/drivers/target/iscsi/iscsi_target_util.c
index 016e882..eeeea38 100644
--- a/drivers/target/iscsi/iscsi_target_util.c
+++ b/drivers/target/iscsi/iscsi_target_util.c
@@ -722,21 +722,23 @@ 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) {
- se_cmd = &cmd->se_cmd;
- __iscsit_free_cmd(cmd, true, shutdown);
+ op_scsi = true;
* Fallthrough
- 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->se_sess, se_cmd);