target: Avoid early CMD_T_PRE_EXECUTE failures during ABORT_TASK

This patch fixes bug where early se_cmd exceptions that occur
before backend execution can result in use-after-free if/when
a subsequent ABORT_TASK occurs for the same tag.

Since an early se_cmd exception will have had se_cmd added to
se_session->sess_cmd_list via target_get_sess_cmd(), it will
not have CMD_T_COMPLETE set by the usual target_complete_cmd()
backend completion path.

This causes a subsequent ABORT_TASK + __target_check_io_state()
to signal ABORT_TASK should proceed.  As core_tmr_abort_task()
executes, it will bring the outstanding se_cmd->cmd_kref count
down to zero releasing se_cmd, after se_cmd has already been
queued with error status into fabric driver response path code.

To address this bug, introduce a CMD_T_PRE_EXECUTE bit that is
set at target_get_sess_cmd() time, and cleared immediately before
backend driver dispatch in target_execute_cmd() once CMD_T_ACTIVE
is set.

Then, check CMD_T_PRE_EXECUTE within __target_check_io_state() to
determine when an early exception has occured, and avoid aborting
this se_cmd since it will have already been queued into fabric
driver response path code.

Reported-by: Donald White <dew@datera.io>
Cc: Donald White <dew@datera.io>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: stable@vger.kernel.org # 3.14+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index d3139a95ea77..ccf501b8359c 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -490,6 +490,7 @@ struct se_cmd {
 #define CMD_T_STOP		(1 << 5)
 #define CMD_T_TAS		(1 << 10)
 #define CMD_T_FABRIC_STOP	(1 << 11)
+#define CMD_T_PRE_EXECUTE	(1 << 12)
 	spinlock_t		t_state_lock;
 	struct kref		cmd_kref;
 	struct completion	t_transport_stop_comp;