[PATCH] can: raw: fix ro->uniq use-after-free in raw_rcv()

[Oliver Hartkopp <socketcan@hartkopp.net>]

From: Samuel Page <sam@bynar.io>

raw_release() unregisters raw CAN receive filters via can_rx_unregister(),
but receiver deletion is deferred with call_rcu(). This leaves a window
where raw_rcv() may still be running in an RCU read-side critical section
after raw_release() frees ro->uniq, leading to a use-after-free of the
percpu uniq storage.

Move free_percpu(ro->uniq) out of raw_release() and into a raw-specific
socket destructor. can_rx_unregister() takes an extra reference to the
socket and only drops it from the RCU callback, so freeing uniq from
sk_destruct ensures the percpu area is not released until the relevant
callbacks have drained.

Fixes: 514ac99c64b2 ("can: fix multiple delivery of a single CAN frame for overlapping CAN filters")
Cc: stable@vger.kernel.org # v4.1+
Assisted-by: Bynario AI
Signed-off-by: Samuel Page <sam@bynar.io>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/raw.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index eee244ffc31e..58a96e933deb 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -361,6 +361,14 @@ static int raw_notifier(struct notifier_block *nb, unsigned long msg,
 	return NOTIFY_DONE;
 }
 
+static void raw_sock_destruct(struct sock *sk)
+{
+	struct raw_sock *ro = raw_sk(sk);
+
+	free_percpu(ro->uniq);
+	can_sock_destruct(sk);
+}
+
 static int raw_init(struct sock *sk)
 {
 	struct raw_sock *ro = raw_sk(sk);
@@ -387,6 +395,8 @@ static int raw_init(struct sock *sk)
 	if (unlikely(!ro->uniq))
 		return -ENOMEM;
 
+	sk->sk_destruct = raw_sock_destruct;
+
 	/* set notifier */
 	spin_lock(&raw_notifier_lock);
 	list_add_tail(&ro->notifier, &raw_notifier_list);
@@ -436,7 +446,6 @@ static int raw_release(struct socket *sock)
 	ro->bound = 0;
 	ro->dev = NULL;
 	ro->count = 0;
-	free_percpu(ro->uniq);
 
 	sock_orphan(sk);
 	sock->sk = NULL;
-- 
2.53.0