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: add6746124 ("netfilter: add struct net * to target parameters")
Reported-by: syzbot+d7358a458d8a81aee898@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
1b789577f6