target/iscsi: Fix a race condition in iscsit_add_reject_from_cmd()

BugLink: http://bugs.launchpad.net/bugs/1745052

[ Upstream commit cfe2b621 ]

Avoid that cmd->se_cmd.se_tfo is read after a command has already been
freed.
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Mike Christie <mchristi@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/target/iscsi/iscsi_target.c

@@ -674,6 +674,7 @@ static int iscsit_add_reject_from_cmd(
 	unsigned char *buf)
 {
 	struct iscsi_conn *conn;
+	const bool do_put = cmd->se_cmd.se_tfo != NULL;
 
 	if (!cmd->conn) {
 		pr_err("cmd->conn is NULL for ITT: 0x%08x\n",
@@ -704,7 +705,7 @@ static int iscsit_add_reject_from_cmd(
 	 * Perform the kref_put now if se_cmd has already been setup by
 	 * scsit_setup_scsi_cmd()
 	 */
-	if (cmd->se_cmd.se_tfo != NULL) {
+	if (do_put) {
 		pr_debug("iscsi reject: calling target_put_sess_cmd >>>>>>\n");
 		target_put_sess_cmd(&cmd->se_cmd);
 	}