Error when executing iptables code “Error commit: Protocol wrong type for socket”

Question

The C code below is equivalent to the following iptables command:

ip6tables -A OUTPUT -t mangle -s 2001:db8:222:2::/64 -j MARK --set-mark 20

However, the iptables command is working fine from the command line but when I execute the code it gives the error

Error commit: Protocol wrong type for socket   

although it is compiled successfully. I have also tried it with setting the DSCP value and it worked fine, so I guess something missing for the MARK module

Linux kernel 3.8.2
iptables version 1.4.12 (I also tried 1.4.21 but didn't work)

The code

struct ip6tc_handle *h;
const ip6t_chainlabel chain = "OUTPUT";
const char *tablename = "mangle";

struct ip6t_entry * e;
struct ip6t_entry_target * target;
struct xt_mark_tginfo2 *pmark;
unsigned int size_ip6t_entry, size_ip6t_entry_target,  size_pmark, total_length; 

size_ip6t_entry = XT_ALIGN(sizeof(struct ip6t_entry));
size_ip6t_entry_target = XT_ALIGN(sizeof(struct ip6t_entry_target));
size_pmark = XT_ALIGN(sizeof(struct xt_mark_tginfo2));

total_length =  size_ip6t_entry +  size_ip6t_entry_target + size_pmark ;


e = calloc(1, total_length);
if(e == NULL)
{
        printf("malloc failure");
        exit(1);
}

//offsets to the other bits:
//target struct begining
e->target_offset = size_ip6t_entry ;
//next "e" struct, end of the current one
e->next_offset = total_length;


char *temps = malloc(128);
temps = "2001:db8:222:2::";
inet_pton(AF_INET6, temps, &e->ipv6.src);
char *temps2 = malloc(128);
temps2 = "FFFF:FFFF:FFFF:FFFF::";
inet_pton(AF_INET6, temps2, &e->ipv6.smsk);
 //e->ipv6.proto = 58 ;
//strcpy(e->ipv6.iniface, "wlan1");


//target struct
target = (struct ip6t_entry_target *) e->elems; 
target->u.target_size = size_ip6t_entry_target;
strcpy(target->u.user.name, "MARK");

 pmark = (struct xt_mark_tginfo2 *) target->data;
 pmark->mark = 0x14;
 pmark->mask = 0xff;


h = ip6tc_init(tablename);
if ( !h )
{
      printf("Error initializing: %s\n", iptc_strerror(errno));
      exit(errno);
}

 int x = ip6tc_append_entry(chain, e, h);

if (!x)
{
        printf("Error append_entry: %s\n", iptc_strerror(errno));
        exit(errno);
}
printf("%s", target->data);
int y = ip6tc_commit(h);
if (!y)
{
        printf("Error commit: %s\n", iptc_strerror(errno));
        exit(errno);
}

exit(0);

Any ideas? Thanks

Answer 1

Late reply, but would like to give a hint to prospective seekers.

Some targets(matches too) require to set correct revision, for xt_mark_tginfo2 I see it must be either 1 or 2.

Another thing is entry (ip6t_entry) flags e.g. I have struggled with reject target (ip6t_reject_info) and I only later found out that entry flag must be set to IP6T_F_PROTO.

I'm not entirely sure, but a hint maybe to have a look at a .family from the xtables_target structure.

Good luck for iptc library fighters ;)