staging: lustre: separate a connection destroy from free struct kib_conn

The logic of the original commit 4d99b2581eff ("staging: lustre: avoid
intensive reconnecting for ko2iblnd") was assumed conditional free of
struct kib_conn if the second argument free_conn in function
kiblnd_destroy_conn(struct kib_conn *conn, bool free_conn) is true.
But this hunk of code was dropped from original commit. As result the logic
works wrong and current code use struct kib_conn after free.

> drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd_cb.c
> 3317  kiblnd_destroy_conn(conn, !peer);
>                           ^^^^ Freed always (but should be conditionally)
> 3318
> 3319  spin_lock_irqsave(lock, flags);
> 3320  if (!peer)
> 3321      continue;
> 3322
> 3323  conn->ibc_peer = peer;
>       ^^^^^^^^^^^^^^ Use after free
> 3324  if (peer->ibp_reconnected < KIB_RECONN_HIGH_RACE)
> 3325      list_add_tail(&conn->ibc_list,
>                          ^^^^^^^^^^^^^^ Use after free
> 3326                    &kiblnd_data.kib_reconn_list);
> 3327  else
> 3328      list_add_tail(&conn->ibc_list,
>                          ^^^^^^^^^^^^^^ Use after free
> 3329                    &kiblnd_data.kib_reconn_wait);

To avoid confusion this fix moved the freeing a struct kib_conn outside of
the function kiblnd_destroy_conn() and free as it was intended in original
commit.

Cc: <stable@vger.kernel.org> # v4.6
Fixes: 4d99b2581eff ("staging: lustre: avoid intensive reconnecting for ko2iblnd")
Signed-off-by: Dmitry Eremin <Dmitry.Eremin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.c

@@ -824,14 +824,15 @@ struct kib_conn *kiblnd_create_conn(struct kib_peer *peer, struct rdma_cm_id *cm
 	return conn;
 
  failed_2:
-	kiblnd_destroy_conn(conn, true);
+	kiblnd_destroy_conn(conn);
+	kfree(conn);
  failed_1:
 	kfree(init_qp_attr);
  failed_0:
 	return NULL;
 }
 
-void kiblnd_destroy_conn(struct kib_conn *conn, bool free_conn)
+void kiblnd_destroy_conn(struct kib_conn *conn)
 {
 	struct rdma_cm_id *cmid = conn->ibc_cmid;
 	struct kib_peer *peer = conn->ibc_peer;
@@ -889,8 +890,6 @@ void kiblnd_destroy_conn(struct kib_conn *conn, bool free_conn)
 		rdma_destroy_id(cmid);
 		atomic_dec(&net->ibn_nconns);
 	}
-
-	kfree(conn);
 }
 
 int kiblnd_close_peer_conns_locked(struct kib_peer *peer, int why)

drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd.h

@@ -1016,7 +1016,7 @@ int  kiblnd_close_peer_conns_locked(struct kib_peer *peer, int why);
 struct kib_conn *kiblnd_create_conn(struct kib_peer *peer,
 				    struct rdma_cm_id *cmid,
 				    int state, int version);
-void kiblnd_destroy_conn(struct kib_conn *conn, bool free_conn);
+void kiblnd_destroy_conn(struct kib_conn *conn);
 void kiblnd_close_conn(struct kib_conn *conn, int error);
 void kiblnd_close_conn_locked(struct kib_conn *conn, int error);
 

drivers/staging/lustre/lnet/klnds/o2iblnd/o2iblnd_cb.c

@@ -3314,11 +3314,13 @@ kiblnd_connd(void *arg)
 			spin_unlock_irqrestore(lock, flags);
 			dropped_lock = 1;
 
-			kiblnd_destroy_conn(conn, !peer);
+			kiblnd_destroy_conn(conn);
 
 			spin_lock_irqsave(lock, flags);
-			if (!peer)
+			if (!peer) {
+				kfree(conn);
 				continue;
+			}
 
 			conn->ibc_peer = peer;
 			if (peer->ibp_reconnected < KIB_RECONN_HIGH_RACE)