Code: check_entry_size_and_hooks(struct ipt_entry *e,
			   struct xt_table_info *newinfo,
			   const unsigned char *base,
			   const unsigned char *limit,
			   const unsigned int *hook_entries,
			   const unsigned int *underflows,
			   unsigned int valid_hooks)
{
	unsigned int h;
	int err;

	if ((unsigned long)e % __alignof__(struct ipt_entry) != 0 ||
	    (unsigned char *)e + sizeof(struct ipt_entry) >= limit ||
	    (unsigned char *)e + e->next_offset > limit) {
		duprintf("Bad offset %p\n", e);
		return -EINVAL;
	}

	if (e->next_offset
	    < sizeof(struct ipt_entry) + sizeof(struct xt_entry_target)) {
		duprintf("checking: element %p size %u\n",
			 e, e->next_offset);
		return -EINVAL;
	}

 	if (!ip_checkentry(&e->ip))
 		return -EINVAL;
 
	err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
 	if (err)
 		return err;
 
	/* Check hooks & underflows */
	for (h = 0; h < NF_INET_NUMHOOKS; h++) {
		if (!(valid_hooks & (1 << h)))
			continue;
		if ((unsigned char *)e - base == hook_entries[h])
			newinfo->hook_entry[h] = hook_entries[h];
		if ((unsigned char *)e - base == underflows[h]) {
			if (!check_underflow(e)) {
				pr_debug("Underflows must be unconditional and "
					 "use the STANDARD target with "
					 "ACCEPT/DROP\n");
				return -EINVAL;
			}
			newinfo->underflow[h] = underflows[h];
		}
	}

	/* Clear counters and comefrom */
	e->counters = ((struct xt_counters) { 0, 0 });
	e->comefrom = 0;
	return 0;
}

Commit Message: netfilter: x_tables: check for bogus target offset

We're currently asserting that targetoff + targetsize <= nextoff.

Extend it to also check that targetoff is >= sizeof(xt_entry).
Since this is generic code, add an argument pointing to the start of the
match/target, we can then derive the base structure size from the delta.

We also need the e->elems pointer in a followup change to validate matches.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
CWE ID: CWE-264
check_entry_size_and_hooks(struct ipt_entry *e,
			   struct xt_table_info *newinfo,
			   const unsigned char *base,
			   const unsigned char *limit,
			   const unsigned int *hook_entries,
			   const unsigned int *underflows,
			   unsigned int valid_hooks)
{
	unsigned int h;
	int err;

	if ((unsigned long)e % __alignof__(struct ipt_entry) != 0 ||
	    (unsigned char *)e + sizeof(struct ipt_entry) >= limit ||
	    (unsigned char *)e + e->next_offset > limit) {
		duprintf("Bad offset %p\n", e);
		return -EINVAL;
	}

	if (e->next_offset
	    < sizeof(struct ipt_entry) + sizeof(struct xt_entry_target)) {
		duprintf("checking: element %p size %u\n",
			 e, e->next_offset);
		return -EINVAL;
	}

 	if (!ip_checkentry(&e->ip))
 		return -EINVAL;
 
	err = xt_check_entry_offsets(e, e->elems, e->target_offset,
				     e->next_offset);
 	if (err)
 		return err;
 
	/* Check hooks & underflows */
	for (h = 0; h < NF_INET_NUMHOOKS; h++) {
		if (!(valid_hooks & (1 << h)))
			continue;
		if ((unsigned char *)e - base == hook_entries[h])
			newinfo->hook_entry[h] = hook_entries[h];
		if ((unsigned char *)e - base == underflows[h]) {
			if (!check_underflow(e)) {
				pr_debug("Underflows must be unconditional and "
					 "use the STANDARD target with "
					 "ACCEPT/DROP\n");
				return -EINVAL;
			}
			newinfo->underflow[h] = underflows[h];
		}
	}

	/* Clear counters and comefrom */
	e->counters = ((struct xt_counters) { 0, 0 });
	e->comefrom = 0;
	return 0;
}
