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[4.4,4.9] can: bcm: delay release of struct bcm_op after synchronize_rcu()

Message ID 20210712153036.5937-2-socketcan@hartkopp.net
State New
Headers show
Series [4.4,4.9] can: bcm: delay release of struct bcm_op after synchronize_rcu() | expand

Commit Message

Oliver Hartkopp July 12, 2021, 3:30 p.m. UTC 
From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

commit d5f9023fa61ee8b94f37a93f08e94b136cf1e463 upstream.

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/20210619161813.2098382-1-cascardo@canonical.com
Cc: linux-stable <stable@vger.kernel.org>
Reported-by: syzbot+0f7e7e5e2f4f40fa89c0@syzkaller.appspotmail.com
Reported-by: Norbert Slusarek <nslusarek@gmx.net>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 net/can/bcm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/net/can/bcm.c b/net/can/bcm.c
index c6fee58baac4..3e131dc5f0e5 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -811,10 +811,11 @@  static int bcm_delete_rx_op(struct list_head *ops, canid_t can_id, int ifindex)
 				can_rx_unregister(NULL, op->can_id,
 						  REGMASK(op->can_id),
 						  bcm_rx_handler, op);
 
 			list_del(&op->list);
+			synchronize_rcu();
 			bcm_remove_op(op);
 			return 1; /* done */
 		}
 	}
 
@@ -1536,13 +1537,17 @@  static int bcm_release(struct socket *sock)
 		} else
 			can_rx_unregister(NULL, op->can_id,
 					  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);
+
 	/* remove procfs entry */
 	if (proc_dir && bo->bcm_proc_read)
 		remove_proc_entry(bo->procname, proc_dir);
 
 	/* remove device reference */