NULL Check

post.c

@@ -17,6 +17,7 @@
 #include <net/checksum.h>
 #define DRIVER_AUTHOR "a_r_g_v"
 #define DRIVER_DESC "sugoi"
+#define ADD_VLAN 50
 
 static struct nf_hook_ops arp_in_nfho;
 static struct nf_hook_ops arp_out_nfho;
@@ -77,12 +78,18 @@ static unsigned int arp_in_hook_func(void *priv,
 			// TCP Rewrite Checksum
 			if(iph->protocol == 0x6) {
 				struct tcphdr *tcph = tcp_hdr(skb);
+                                if(tcph == NULL || tcph->check == NULL) {
+                                    return NF_ACCEPT;
+                                  }
 				csum_replace2(&tcph->check, iph->daddr, htonl(daddr));
 				//printk(KERN_INFO "[After TCP DEST] tcp_check: %08x, old_check: %08x \n", tcph->check, old_check);
 			} 
 			// UDP Rewrite Checksum
 			else if (iph->protocol == 17) {
 				struct udphdr *udph = udp_hdr(skb);
+                                if(udph == NULL || udph->check == NULL) {
+                                    return NF_ACCEPT;
+                                  }
 				csum_replace2(&udph->check, iph->daddr, htonl(daddr));
 				//printk(KERN_INFO "[After UDP DEST] udp_check: %08x, old_check: %08x \n", udph->check, old_check);
 			}
@@ -100,11 +107,17 @@ static unsigned int arp_in_hook_func(void *priv,
 			// TCP, Calucate Checksum
 			if(iph->protocol == 0x6) {
 				struct tcphdr *tcph = tcp_hdr(skb);
+                                if(tcph == NULL || tcph->check == NULL) {
+                                  return NF_ACCEPT;
+                                }
 				csum_replace2(&tcph->check, iph->saddr, htonl(saddr));
 				//printk(KERN_INFO "[After TCP SRC] tcp_check: %08x, old_check: %08x \n", tcph->check, old_check);
 			// UDP, Calucate Checksum
 			} else if (iph->protocol == 17) {
 				struct udphdr *udph = udp_hdr(skb);
+                                if(udph == NULL || udph->check == NULL) {
+                                  return NF_ACCEPT;
+                                }
 				csum_replace2(&udph->check, iph->saddr, htonl(saddr));
 				//printk(KERN_INFO "[After UDP SRC] udp_check: %08x, old_check: %08x \n", udph->check, old_check);
 			}
@@ -114,7 +127,7 @@ static unsigned int arp_in_hook_func(void *priv,
 		}
 		if(flag){
 
-			skb->vlan_tci += 2015;
+			skb->vlan_tci += 2000 + ADD_VLAN;
 		}
 
 
@@ -143,7 +156,7 @@ static unsigned int arp_in_hook_func(void *priv,
 				arpb->saddr[0] == 192 && arpb->saddr[1] == 168) {
 			arpb->daddr[0] = arpb->saddr[0] = 10;
 			arpb->daddr[1] = arpb->saddr[1] = team_id;
-			skb->vlan_tci += 2015;
+			skb->vlan_tci += 2000 + ADD_VLAN;
 		}
 
 		//printk(KERN_INFO "[After ARP IN] daddr %pI4, saddr %pI4 in:%s vlan_id: %d, team_id: %d \n", arpb->daddr, arpb->saddr, state->in->name, vlan_id, team_id);
@@ -165,7 +178,7 @@ static unsigned int arp_out_hook_func(void *priv,
 	// IP
 	if (ehdr->h_proto == 0x0008) {
 		struct iphdr *iph = ip_hdr(skb);
-		if (iph == NULL) {
+		if (iph == NULL || iph->daddr == NULL || iph->saddr == NULL) {
 			return NF_ACCEPT;
 		}
 
@@ -198,19 +211,25 @@ static unsigned int arp_out_hook_func(void *priv,
 			csum_replace2(&iph->check, iph->saddr, htonl(saddr));
 			if(iph->protocol == 0x6) {
 				struct tcphdr *tcph = tcp_hdr(skb);
-				csum_replace2(&tcph->check, iph->daddr, htonl(daddr));
+                                if (tcph == NULL || tcph->check == NULL ) {
+                                    return NF_ACCEPT; 
+                                }
+				csum_replace2(&tcph->check, iph->saddr, htonl(saddr));
 				//printk(KERN_INFO "[After TCP DEST] tcp_check: %08x, old_check: %08x \n", tcph->check, old_check);
 			} else if (iph->protocol == 17) {
 				struct udphdr *udph = udp_hdr(skb);
-				csum_replace2(&udph->check, iph->daddr, htonl(daddr));
+                                if (udph == NULL || udph->check == NULL ) {
+                                    return NF_ACCEPT; 
+                                }
+				csum_replace2(&udph->check, iph->saddr, htonl(saddr));
 				//printk(KERN_INFO "[After UDP DEST] udp_check: %08x, old_check: %08x \n", udph->check, old_check);
 			}
 			iph->saddr = htonl(saddr);
 			flag = true;
 
 		}
 		if(flag) {
-			skb->vlan_tci -= 15;	
+			skb->vlan_tci -= ADD_VLAN;	
 		}
 		if (vlan_id >= 2000) {
 			skb->vlan_tci -= 2000;
@@ -243,7 +262,7 @@ static unsigned int arp_out_hook_func(void *priv,
 				arpb->saddr[0] == 10 && arpb->saddr[1] >= 0 && arpb->saddr[1] <= 15 ) {
 			arpb->daddr[0] = arpb->saddr[0] = 192;
 			arpb->daddr[1] = arpb->saddr[1] = 168;
-			skb->vlan_tci -= 15;
+			skb->vlan_tci -= ADD_VLAN;
 		}