can: Fix CAN_(EFF|RTR)_FLAG handling in can_filter

Due to a wrong safety check in af_can.c it was not possible to filter
for SFF frames with a specific CAN identifier without getting the
same selected CAN identifier from a received EFF frame also.

This fix has a minimum (but user visible) impact on the CAN filter
API and therefore the CAN version is set to a new date.

Indeed the 'old' API is still working as-is. But when now setting
CAN_(EFF|RTR)_FLAG in can_filter.can_mask you might get less traffic
than before - but still the stuff that you expected to get for your
defined filter ...

Thanks to Kurt Van Dijck for pointing at this issue and for the review.

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Acked-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 48 insertions, 15 deletions

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 7d4d2b3c137e..d8173e50cb87 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -319,23 +319,52 @@ static struct dev_rcv_lists *find_dev_rcv_lists(struct net_device *dev)
         return n ? d : NULL;
 }
 
+/**
+ * find_rcv_list - determine optimal filterlist inside device filter struct
+ * @can_id: pointer to CAN identifier of a given can_filter
+ * @mask: pointer to CAN mask of a given can_filter
+ * @d: pointer to the device filter struct
+ *
+ * Description:
+ *  Returns the optimal filterlist to reduce the filter handling in the
+ *  receive path. This function is called by service functions that need
+ *  to register or unregister a can_filter in the filter lists.
+ *
+ *  A filter matches in general, when
+ *
+ *          <received_can_id> & mask == can_id & mask
+ *
+ *  so every bit set in the mask (even CAN_EFF_FLAG, CAN_RTR_FLAG) describe
+ *  relevant bits for the filter.
+ *
+ *  The filter can be inverted (CAN_INV_FILTER bit set in can_id) or it can
+ *  filter for error frames (CAN_ERR_FLAG bit set in mask). For error frames
+ *  there is a special filterlist and a special rx path filter handling.
+ *
+ * Return:
+ *  Pointer to optimal filterlist for the given can_id/mask pair.
+ *  Constistency checked mask.
+ *  Reduced can_id to have a preprocessed filter compare value.
+ */
 static struct hlist_head *find_rcv_list(canid_t *can_id, canid_t *mask,
                                         struct dev_rcv_lists *d)
 {
         canid_t inv = *can_id & CAN_INV_FILTER; /* save flag before masking */
 
-        /* filter error frames */
+        /* filter for error frames in extra filterlist */
         if (*mask & CAN_ERR_FLAG) {
-                /* clear CAN_ERR_FLAG in list entry */
+                /* clear CAN_ERR_FLAG in filter entry */
                 *mask &= CAN_ERR_MASK;
                 return &d->rx[RX_ERR];
         }
 
-        /* ensure valid values in can_mask */
-        if (*mask & CAN_EFF_FLAG)
-                *mask &= (CAN_EFF_MASK | CAN_EFF_FLAG | CAN_RTR_FLAG);
-        else
-                *mask &= (CAN_SFF_MASK | CAN_RTR_FLAG);
+        /* with cleared CAN_ERR_FLAG we have a simple mask/value filterpair */
+
+#define CAN_EFF_RTR_FLAGS (CAN_EFF_FLAG | CAN_RTR_FLAG)
+
+        /* ensure valid values in can_mask for 'SFF only' frame filtering */
+        if ((*mask & CAN_EFF_FLAG) && !(*can_id & CAN_EFF_FLAG))
+                *mask &= (CAN_SFF_MASK | CAN_EFF_RTR_FLAGS);
 
         /* reduce condition testing at receive time */
         *can_id &= *mask;
@@ -348,15 +377,19 @@ static struct hlist_head *find_rcv_list(canid_t *can_id, canid_t *mask,
         if (!(*mask))
                 return &d->rx[RX_ALL];
 
-        /* use extra filterset for the subscription of exactly *ONE* can_id */
-        if (*can_id & CAN_EFF_FLAG) {
-                if (*mask == (CAN_EFF_MASK | CAN_EFF_FLAG)) {
-                        /* RFC: a use-case for hash-tables in the future? */
-                        return &d->rx[RX_EFF];
+        /* extra filterlists for the subscription of a single non-RTR can_id */
+        if (((*mask & CAN_EFF_RTR_FLAGS) == CAN_EFF_RTR_FLAGS)
+            && !(*can_id & CAN_RTR_FLAG)) {
+
+                if (*can_id & CAN_EFF_FLAG) {
+                        if (*mask == (CAN_EFF_MASK | CAN_EFF_RTR_FLAGS)) {
+                                /* RFC: a future use-case for hash-tables? */
+                                return &d->rx[RX_EFF];
+                        }
+                } else {
+                        if (*mask == (CAN_SFF_MASK | CAN_EFF_RTR_FLAGS))
+                                return &d->rx_sff[*can_id];
                 }
-        } else {
-                if (*mask == CAN_SFF_MASK)
-                        return &d->rx_sff[*can_id];
         }
 
         /* default: filter via can_id/can_mask */