netfilter: x_tables: validate e->target_offset early

commit bdf533de6968e9686df777dc178486f600c6e617 upstream.

We should check that e->target_offset is sane before
mark_source_chains gets called since it will fetch the target entry
for loop detection.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc net/ipv4/netfilter/arp_tables.c
Simple merge

diff --cc net/ipv4/netfilter/ip_tables.c
Simple merge

diff --cc net/ipv6/netfilter/ip6_tables.c
Simple merge