[PATCH RFC v2 1/2] can: fix multiple delivery of a single CAN frame for overlapping CAN filters

[Oliver Hartkopp <socketcan@hartkopp.net>]

The CAN_RAW socket can set multiple CAN identifier specific filters that lead
to multiple filters in the af_can.c filter processing. These filters are
indenpendent from each other which leads to logical OR'ed filters when applied.

This patch makes sure that every CAN frame which is filtered for a specific
socket is only delivered once to the user space. This is independent from the
number of matching CAN filters of this socket.

As the can_raw() function is executed from NET_RX softirq the introduced
variables are implemented as per-CPU variables to avoid extensive locking at
CAN frame reception time.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/raw.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/net/can/raw.c b/net/can/raw.c
index 00c13ef..866a9b3 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -86,6 +86,8 @@ struct raw_sock {
 	struct can_filter dfilter; /* default/single filter */
 	struct can_filter *filter; /* pointer to filter(s) */
 	can_err_mask_t err_mask;
+	struct sk_buff __percpu **uniq_skb;
+	ktime_t __percpu *uniq_tstamp;
 };
 
 /*
@@ -123,6 +125,15 @@ static void raw_rcv(struct sk_buff *oskb, void *data)
 	if (!ro->fd_frames && oskb->len != CAN_MTU)
 		return;
 
+	/* eliminate multiple filter matches for the same skb */
+	if (*this_cpu_ptr(ro->uniq_skb) == oskb &&
+	    ktime_equal(*this_cpu_ptr(ro->uniq_tstamp), oskb->tstamp)) {
+			return;
+	} else {
+		*this_cpu_ptr(ro->uniq_skb) = oskb;
+		*this_cpu_ptr(ro->uniq_tstamp) = oskb->tstamp;
+	}
+
 	/* clone the given skb to be able to enqueue it into the rcv queue */
 	skb = skb_clone(oskb, GFP_ATOMIC);
 	if (!skb)
@@ -282,6 +293,7 @@ static int raw_notifier(struct notifier_block *nb,
 static int raw_init(struct sock *sk)
 {
 	struct raw_sock *ro = raw_sk(sk);
+	int cpu;
 
 	ro->bound            = 0;
 	ro->ifindex          = 0;
@@ -297,6 +309,20 @@ static int raw_init(struct sock *sk)
 	ro->recv_own_msgs    = 0;
 	ro->fd_frames        = 0;
 
+	ro->uniq_skb = alloc_percpu(struct sk_buff *);
+	if (unlikely(ro->uniq_skb == NULL))
+		return -ENOMEM;
+	for_each_possible_cpu(cpu)
+		*per_cpu_ptr(ro->uniq_skb, cpu) = NULL;
+
+	ro->uniq_tstamp = alloc_percpu(ktime_t);
+	if (unlikely(ro->uniq_tstamp == NULL)) {
+		free_percpu(ro->uniq_skb);
+		return -ENOMEM;
+	}
+	for_each_possible_cpu(cpu)
+		*per_cpu_ptr(ro->uniq_tstamp, cpu) = ktime_set(0, 0);
+
 	/* set notifier */
 	ro->notifier.notifier_call = raw_notifier;
 
@@ -339,6 +365,8 @@ static int raw_release(struct socket *sock)
 	ro->ifindex = 0;
 	ro->bound   = 0;
 	ro->count   = 0;
+	free_percpu(ro->uniq_skb);
+	free_percpu(ro->uniq_tstamp);
 
 	sock_orphan(sk);
 	sock->sk = NULL;
-- 
2.1.4