Re: libiptc ... and matches , seg fault

[Francesco Ciocchetti <primero@fastwebnet.it>]

Tomáš Macek wrote:

> The strcmp() function will try to compare/get the 0x0 memory pointed
> by the me->version pointer and this (in the strcmp() function) raises
> the sigseg error.


Yes :)

> You could try this:
>
> if (me->version != NULL && strcmp(me->version, program_version) != 0) {
> ...
> }
>
> If the first condition "if (me->version != NULL)" failes, the rest
> will be not processed.
>
My problem is that the "register_match" function is not a function of my
program, but a function from iptables.c that is called by init function
in libipt_tcp.c ... what i'm wondering now is why my "me->version" could
be or is NULL or maybe program_version could be NULL too.

this is the extract from libipt_tcp.c

static
struct iptables_match tcp
= { NULL,
"tcp",
IPTABLES_VERSION,
IPT_ALIGN(sizeof(struct ipt_tcp)),
IPT_ALIGN(sizeof(struct ipt_tcp)),
&help,
&init,
&parse,
&final_check,
&print,
&save,
opts };

void
_init(void)
{
register_match(&tcp);
}



so it seems that the field version of tcp structure is filled, at
compilation time, by IPTABLES_VERSION ...

what i do in my program is just a call to

find_match("tcp",TRY_LOAD,&matches)

where matches is just :

struct iptables_rule_match *matches = NULL;


as is done in iptables.c ...



bye
Francesco