can: cangw: introduce optional uid to reference created routing jobs

Similar to referencing iptables rules by their line number this UID allows to
reference created routing jobs, e.g. to alter configured data modifications.

The UID is an optional non-zero value which can be provided at routing job
creation time. When the UID is set the UID replaces the data modification
configuration as job identification attribute e.g. at job removal time.

Signed-off-by: Oliver Hartkopp <[e-mail]>
Signed-off-by: Marc Kleine-Budde <[e-mail]>

include/uapi/linux/can/gw.h

···
 	CGW_FILTER,	/* specify struct can_filter on source CAN device */
 	CGW_DELETED,	/* number of deleted CAN frames (see max_hops param) */
 	CGW_LIM_HOPS,	/* limit the number of hops of this specific rule */
+	CGW_MOD_UID,	/* user defined identifier for modification updates */
 	__CGW_MAX
 };
 
···
  * frame can be processed as much as 'max_hops' times (which is given at module
  * load time of the can-gw module). This value is used to reduce the number of
  * possible hops for this gateway rule to a value smaller then max_hops.
+ *
+ * CGW_MOD_UID (length 4 bytes):
+ * Optional non-zero user defined routing job identifier to alter existing
+ * modification settings at runtime.
  *
  * CGW_CS_XOR (length 4 bytes):
  * Set a simple XOR checksum starting with an initial value into

net/can/gw.c

···
 		void (*xor)(struct can_frame *cf, struct cgw_csum_xor *xor);
 		void (*crc8)(struct can_frame *cf, struct cgw_csum_crc8 *crc8);
 	} csumfunc;
+	u32 uid;
 };
 
 
···
 			goto cancel;
 	}
 
+	if (gwj->mod.uid) {
+		if (nla_put_u32(skb, CGW_MOD_UID, gwj->mod.uid) < 0)
+			goto cancel;
+	}
+
 	if (gwj->mod.csumfunc.crc8) {
 		if (nla_put(skb, CGW_CS_CRC8, CGW_CS_CRC8_LEN,
 			    &gwj->mod.csum.crc8) < 0)
···
 	[CGW_DST_IF]	= { .type = NLA_U32 },
 	[CGW_FILTER]	= { .len = sizeof(struct can_filter) },
 	[CGW_LIM_HOPS]	= { .type = NLA_U8 },
+	[CGW_MOD_UID]	= { .type = NLA_U32 },
 };
 
 /* check for common and gwtype specific attributes */
···
 			else
 				mod->csumfunc.xor = cgw_csum_xor_neg;
 		}
+
+		if (tb[CGW_MOD_UID]) {
+			nla_memcpy(&mod->uid, tb[CGW_MOD_UID], sizeof(u32));
+		}
 	}
 
 	if (gwtype == CGW_TYPE_CAN_CAN) {
···
 {
 	struct rtcanmsg *r;
 	struct cgw_job *gwj;
+	struct cf_mod mod;
+	struct can_can_gw ccgw;
 	u8 limhops = 0;
 	int err = 0;
 
···
 	if (r->gwtype != CGW_TYPE_CAN_CAN)
 		return -EINVAL;
 
+	err = cgw_parse_attr(nlh, &mod, CGW_TYPE_CAN_CAN, &ccgw, &limhops);
+	if (err < 0)
+		return err;
+
+	if (mod.uid) {
+
+		ASSERT_RTNL();
+
+		/* check for updating an existing job with identical uid */
+		hlist_for_each_entry(gwj, &cgw_list, list) {
+
+			if (gwj->mod.uid != mod.uid)
+				continue;
+
+			/* interfaces & filters must be identical */
+			if (memcmp(&gwj->ccgw, &ccgw, sizeof(ccgw)))
+				return -EINVAL;
+
+			/* update modifications with disabled softirq & quit */
+			local_bh_disable();
+			memcpy(&gwj->mod, &mod, sizeof(mod));
+			local_bh_enable();
+			return 0;
+		}
+	}
+
+	/* ifindex == 0 is not allowed for job creation */
+	if (!ccgw.src_idx || !ccgw.dst_idx)
+		return -ENODEV;
+
 	gwj = kmem_cache_alloc(cgw_cache, GFP_KERNEL);
 	if (!gwj)
 		return -ENOMEM;
···
 	gwj->deleted_frames = 0;
 	gwj->flags = r->flags;
 	gwj->gwtype = r->gwtype;
+	gwj->limit_hops = limhops;
 
-	err = cgw_parse_attr(nlh, &gwj->mod, CGW_TYPE_CAN_CAN, &gwj->ccgw,
-			     &limhops);
-	if (err < 0)
-		goto out;
+	/* insert already parsed information */
+	memcpy(&gwj->mod, &mod, sizeof(mod));
+	memcpy(&gwj->ccgw, &ccgw, sizeof(ccgw));
 
 	err = -ENODEV;
-
-	/* ifindex == 0 is not allowed for job creation */
-	if (!gwj->ccgw.src_idx || !gwj->ccgw.dst_idx)
-		goto out;
 
 	gwj->src.dev = __dev_get_by_index(&init_net, gwj->ccgw.src_idx);
 
···
 
 	if (gwj->dst.dev->type != ARPHRD_CAN)
 		goto out;
-
-	gwj->limit_hops = limhops;
 
 	ASSERT_RTNL();
 
···
 		if (gwj->limit_hops != limhops)
 			continue;
 
-		if (memcmp(&gwj->mod, &mod, sizeof(mod)))
-			continue;
+		/* we have a match when uid is enabled and identical */
+		if (gwj->mod.uid || mod.uid) {
+			if (gwj->mod.uid != mod.uid)
+				continue;
+		} else {
+			/* no uid => check for identical modifications */
+			if (memcmp(&gwj->mod, &mod, sizeof(mod)))
+				continue;
+		}
 
 		/* if (r->gwtype == CGW_TYPE_CAN_CAN) - is made sure here */
 		if (memcmp(&gwj->ccgw, &ccgw, sizeof(ccgw)))