ip: frags: Return actual error codes from ip_check_defrag()

Once we wrap ip_check_defrag() in a kfunc, it may be useful for progs to
know the exact error condition ip_check_defrag() encountered.

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>

drivers/net/macvlan.c

@@ -456,7 +456,7 @@ static rx_handler_result_t macvlan_handle_frame(struct sk_buff **pskb)
 		unsigned int hash;
 
 		skb = ip_check_defrag(dev_net(skb->dev), skb, IP_DEFRAG_MACVLAN);
-		if (!skb)
+		if (IS_ERR(skb))
 			return RX_HANDLER_CONSUMED;
 		*pskb = skb;
 		eth = eth_hdr(skb);

net/ipv4/ip_fragment.c

@@ -514,6 +514,7 @@ struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
 	struct iphdr iph;
 	int netoff;
 	u32 len;
+	int err;
 
 	if (skb->protocol != htons(ETH_P_IP))
 		return skb;
@@ -535,15 +536,15 @@ struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
 		if (skb) {
 			if (!pskb_may_pull(skb, netoff + iph.ihl * 4)) {
 				kfree_skb(skb);
-				return NULL;
+				return ERR_PTR(-ENOMEM);
 			}
-			if (pskb_trim_rcsum(skb, netoff + len)) {
+			if ((err = pskb_trim_rcsum(skb, netoff + len))) {
 				kfree_skb(skb);
-				return NULL;
+				return ERR_PTR(err);
 			}
 			memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
-			if (ip_defrag(net, skb, user))
-				return NULL;
+			if ((err = ip_defrag(net, skb, user)))
+				return ERR_PTR(err);
 			skb_clear_hash(skb);
 		}
 	}

net/packet/af_packet.c

@@ -1472,7 +1472,7 @@ static int packet_rcv_fanout(struct sk_buff *skb, struct net_device *dev,
 
 	if (fanout_has_flag(f, PACKET_FANOUT_FLAG_DEFRAG)) {
 		skb = ip_check_defrag(net, skb, IP_DEFRAG_AF_PACKET);
-		if (!skb)
+		if (IS_ERR(skb))
 			return 0;
 	}
 	switch (f->type) {