netfilter: arp_tables: init netns pointer in xt_tgchk_param struct
We get crash when the targets checkentry function tries to make use of the network namespace pointer for arptables. When the net pointer got added back in 2010, only ip/ip6/ebtables were changed to initialize it, so arptables has this set to NULL. This isn't a problem for normal arptables because no existing arptables target has a checkentry function that makes use of par->net. However, direct users of the setsockopt interface can provide any target they want as long as its registered for ARP or UNPSEC protocols. syzkaller managed to send a semi-valid arptables rule for RATEEST target which is enough to trigger NULL deref: kasan: GPF could be caused by NULL-ptr deref or user memory access general protection fault: 0000 [#1] PREEMPT SMP KASAN RIP: xt_rateest_tg_checkentry+0x11d/0xb40 net/netfilter/xt_RATEEST.c:109 [..] xt_check_target+0x283/0x690 net/netfilter/x_tables.c:1019 check_target net/ipv4/netfilter/arp_tables.c:399 [inline] find_check_entry net/ipv4/netfilter/arp_tables.c:422 [inline] translate_table+0x1005/0x1d70 net/ipv4/netfilter/arp_tables.c:572 do_replace net/ipv4/netfilter/arp_tables.c:977 [inline] do_arpt_set_ctl+0x310/0x640 net/ipv4/netfilter/arp_tables.c:1456 Fixes: add67461 ("netfilter: add struct net * to target parameters") Reported-by:<syzbot+d7358a458d8a81aee898@syzkaller.appspotmail.com> Signed-off-by: