netfilter: nf_reject_ipv6: fix nf_reject_ip6_tcphdr_put()

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_reject_ipv6: fix nf_reject_ip6_tcphdr_put()

syzbot reported that nf_reject_ip6_tcphdr_put() was possibly sending
garbage on the four reserved tcp bits (th->res1)

Use skb_put_zero() to clear the whole TCP header,
as done in nf_reject_ip_tcphdr_put()

BUG: KMSAN: uninit-value in nf_reject_ip6_tcphdr_put+0x688/0x6c0 net/ipv6/netfilter/nf_reject_ipv6.c:255
nf_reject_ip6_tcphdr_put+0x688/0x6c0 net/ipv6/netfilter/nf_reject_ipv6.c:255
nf_send_reset6+0xd84/0x15b0 net/ipv6/netfilter/nf_reject_ipv6.c:344
nft_reject_inet_eval+0x3c1/0x880 net/netfilter/nft_reject_inet.c:48
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x438/0x22a0 net/netfilter/nf_tables_core.c:288
nft_do_chain_inet+0x41a/0x4f0 net/netfilter/nft_chain_filter.c:161
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
nf_hook include/linux/netfilter.h:269 [inline]
NF_HOOK include/linux/netfilter.h:312 [inline]
ipv6_rcv+0x29b/0x390 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core net/core/dev.c:5661 [inline]
__netif_receive_skb+0x1da/0xa00 net/core/dev.c:5775
process_backlog+0x4ad/0xa50 net/core/dev.c:6108
__napi_poll+0xe7/0x980 net/core/dev.c:6772
napi_poll net/core/dev.c:6841 [inline]
net_rx_action+0xa5a/0x19b0 net/core/dev.c:6963
handle_softirqs+0x1ce/0x800 kernel/softirq.c:554
__do_softirq+0x14/0x1a kernel/softirq.c:588
do_softirq+0x9a/0x100 kernel/softirq.c:455
__local_bh_enable_ip+0x9f/0xb0 kernel/softirq.c:382
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:908 [inline]
__dev_queue_xmit+0x2692/0x5610 net/core/dev.c:4450
dev_queue_xmit include/linux/netdevice.h:3105 [inline]
neigh_resolve_output+0x9ca/0xae0 net/core/neighbour.c:1565
neigh_output include/net/neighbour.h:542 [inline]
ip6_finish_output2+0x2347/0x2ba0 net/ipv6/ip6_output.c:141
__ip6_finish_output net/ipv6/ip6_output.c:215 [inline]
ip6_finish_output+0xbb8/0x14b0 net/ipv6/ip6_output.c:226
NF_HOOK_COND include/linux/netfilter.h:303 [inline]
ip6_output+0x356/0x620 net/ipv6/ip6_output.c:247
dst_output include/net/dst.h:450 [inline]
NF_HOOK include/linux/netfilter.h:314 [inline]
ip6_xmit+0x1ba6/0x25d0 net/ipv6/ip6_output.c:366
inet6_csk_xmit+0x442/0x530 net/ipv6/inet6_connection_sock.c:135
__tcp_transmit_skb+0x3b07/0x4880 net/ipv4/tcp_output.c:1466
tcp_transmit_skb net/ipv4/tcp_output.c:1484 [inline]
tcp_connect+0x35b6/0x7130 net/ipv4/tcp_output.c:4143
tcp_v6_connect+0x1bcc/0x1e40 net/ipv6/tcp_ipv6.c:333
__inet_stream_connect+0x2ef/0x1730 net/ipv4/af_inet.c:679
inet_stream_connect+0x6a/0xd0 net/ipv4/af_inet.c:750
__sys_connect_file net/socket.c:2061 [inline]
__sys_connect+0x606/0x690 net/socket.c:2078
__do_sys_connect net/socket.c:2088 [inline]
__se_sys_connect net/socket.c:2085 [inline]
__x64_sys_connect+0x91/0xe0 net/socket.c:2085
x64_sys_call+0x27a5/0x3ba0 arch/x86/include/generated/asm/syscalls_64.h:43
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
nf_reject_ip6_tcphdr_put+0x60c/0x6c0 net/ipv6/netfilter/nf_reject_ipv6.c:249
nf_send_reset6+0xd84/0x15b0 net/ipv6/netfilter/nf_reject_ipv6.c:344
nft_reject_inet_eval+0x3c1/0x880 net/netfilter/nft_reject_inet.c:48
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x438/0x22a0 net/netfilter/nf_tables_core.c:288
nft_do_chain_inet+0x41a/0x4f0 net/netfilter/nft_chain_filter.c:161
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xf4/0x400 net/netfilter/core.c:626
nf_hook include/linux/netfilter.h:269 [inline]
NF_HOOK include/linux/netfilter.h:312 [inline]
ipv6_rcv+0x29b/0x390 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core
---truncated---