Code: static inline int check_entry_size_and_hooks(struct arpt_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 arpt_entry) != 0 ||
	    (unsigned char *)e + sizeof(struct arpt_entry) >= limit) {
 		duprintf("Bad offset %p\n", e);
 		return -EINVAL;
 	}

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

	err = check_entry(e);
	if (err)
		return err;

	/* Check hooks & underflows */
	for (h = 0; h < NF_ARP_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_err("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;
}

Vulnerability Type: DoS Overflow +Info 
CWE ID: CWE-119
Summary: The IPT_SO_SET_REPLACE setsockopt implementation in the netfilter subsystem in the Linux kernel before 4.6 allows local users to cause a denial of service (out-of-bounds read) or possibly obtain sensitive information from kernel heap memory by leveraging in-container root access to provide a crafted offset value that leads to crossing a ruleset blob boundary.
Commit Message: netfilter: x_tables: make sure e->next_offset covers remaining blob size

Otherwise this function may read data beyond the ruleset blob.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>