tcm_fc: Fix free-after-use regression in ft_free_cmd

This patch fixes a free-after-use regression in ft_free_cmd(), where
ft_sess_put() is called with cmd->sess after percpu_ida_free() has
already released the tag.

Fix this bug by saving the ft_sess pointer ahead of percpu_ida_free(),
and pass it directly to ft_sess_put().

The regression was originally introduced in v3.13-rc1 commit:

  commit 5f544cfa
  Author: Nicholas Bellinger <nab@daterainc.com>
  Date:   Mon Sep 23 12:12:42 2013 -0700

      tcm_fc: Convert to per-cpu command map pre-allocation of ft_cmd
Reported-by: Jun Wu <jwu@stormojo.com>
Cc: Mark Rustad <mark.d.rustad@intel.com>
Cc: Robert Love <robert.w.love@intel.com>
Cc: <stable@vger.kernel.org> #3.13+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/tcm_fc/tfc_cmd.c

@@ -90,18 +90,18 @@ static void ft_free_cmd(struct ft_cmd *cmd)
 {
 	struct fc_frame *fp;
 	struct fc_lport *lport;
-	struct se_session *se_sess;
+	struct ft_sess *sess;
 
 	if (!cmd)
 		return;
-	se_sess = cmd->sess->se_sess;
+	sess = cmd->sess;
 	fp = cmd->req_frame;
 	lport = fr_dev(fp);
 	if (fr_seq(fp))
 		lport->tt.seq_release(fr_seq(fp));
 	fc_frame_free(fp);
-	percpu_ida_free(&se_sess->sess_tag_pool, cmd->se_cmd.map_tag);
-	ft_sess_put(cmd->sess);	/* undo get from lookup at recv */
+	percpu_ida_free(&sess->se_sess->sess_tag_pool, cmd->se_cmd.map_tag);
+	ft_sess_put(sess);	/* undo get from lookup at recv */
 }
 
 void ft_release_cmd(struct se_cmd *se_cmd)