can: bcm: delay release of struct bcm_op after synchronize_rcu()

can_rx_register() callbacks may be called concurrently to the call to
can_rx_unregister(). The callbacks and callback data, though, are
protected by RCU and the struct sock reference count.

So the callback data is really attached to the life of sk, meaning
that it should be released on sk_destruct. However, bcm_remove_op()
calls tasklet_kill(), and RCU callbacks may be called under RCU
softirq, so that cannot be used on kernels before the introduction of
HRTIMER_MODE_SOFT.

However, bcm_rx_handler() is called under RCU protection, so after
calling can_rx_unregister(), we may call synchronize_rcu() in order to
wait for any RCU read-side critical sections to finish. That is,
bcm_rx_handler() won't be called anymore for those ops. So, we only
free them, after we do that synchronize_rcu().

Fixes: ffd980f976e7 ("[CAN]: Add broadcast manager (bcm) protocol")
Link: https://lore.kernel.org/r/[email protected]
Cc: linux-stable <[email protected]>
Reported-by: [email protected]
Reported-by: Norbert Slusarek <[email protected]>
Signed-off-by: Thadeu Lima de Souza Cascardo <[email protected]>
Acked-by: Oliver Hartkopp <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>

diff --git a/net/can/bcm.c b/net/can/bcm.c
index f3e4d9528fa38787563ddbdce0375e1f417436d8..0928a39c4423bcbca3d03fffc493950162aecb37 100644 (file)
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -785,6 +785,7 @@ static int bcm_delete_rx_op(struct list_head *ops, struct bcm_msg_head *mh,
                                                  bcm_rx_handler, op);
 
                        list_del(&op->list);
+                       synchronize_rcu();
                        bcm_remove_op(op);
                        return 1; /* done */
                }
@@ -1533,9 +1534,13 @@ static int bcm_release(struct socket *sock)
                                          REGMASK(op->can_id),
                                          bcm_rx_handler, op);
 
-               bcm_remove_op(op);
        }
 
+       synchronize_rcu();
+
+       list_for_each_entry_safe(op, next, &bo->rx_ops, list)
+               bcm_remove_op(op);
+
 #if IS_ENABLED(CONFIG_PROC_FS)
        /* remove procfs entry */
        if (net->can.bcmproc_dir && bo->bcm_proc_read)