sched: act_ct: take care of padding in struct zones_ht_key

Blamed commit increased lookup key size from 2 bytes to 16 bytes,
because zones_ht_key got a struct net pointer.

Make sure rhashtable_lookup() is not using the padding bytes
which are not initialized.

 BUG: KMSAN: uninit-value in rht_ptr_rcu include/linux/rhashtable.h:376 [inline]
 BUG: KMSAN: uninit-value in __rhashtable_lookup include/linux/rhashtable.h:607 [inline]
 BUG: KMSAN: uninit-value in rhashtable_lookup include/linux/rhashtable.h:646 [inline]
 BUG: KMSAN: uninit-value in rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
 BUG: KMSAN: uninit-value in tcf_ct_flow_table_get+0x611/0x2260 net/sched/act_ct.c:329
  rht_ptr_rcu include/linux/rhashtable.h:376 [inline]
  __rhashtable_lookup include/linux/rhashtable.h:607 [inline]
  rhashtable_lookup include/linux/rhashtable.h:646 [inline]
  rhashtable_lookup_fast include/linux/rhashtable.h:672 [inline]
  tcf_ct_flow_table_get+0x611/0x2260 net/sched/act_ct.c:329
  tcf_ct_init+0xa67/0x2890 net/sched/act_ct.c:1408
  tcf_action_init_1+0x6cc/0xb30 net/sched/act_api.c:1425
  tcf_action_init+0x458/0xf00 net/sched/act_api.c:1488
  tcf_action_add net/sched/act_api.c:2061 [inline]
  tc_ctl_action+0x4be/0x19d0 net/sched/act_api.c:2118
  rtnetlink_rcv_msg+0x12fc/0x1410 net/core/rtnetlink.c:6647
  netlink_rcv_skb+0x375/0x650 net/netlink/af_netlink.c:2550
  rtnetlink_rcv+0x34/0x40 net/core/rtnetlink.c:6665
  netlink_unicast_kernel net/netlink/af_netlink.c:1331 [inline]
  netlink_unicast+0xf52/0x1260 net/netlink/af_netlink.c:1357
  netlink_sendmsg+0x10da/0x11e0 net/netlink/af_netlink.c:1901
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg+0x30f/0x380 net/socket.c:745
  ____sys_sendmsg+0x877/0xb60 net/socket.c:2597
  ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2651
  __sys_sendmsg net/socket.c:2680 [inline]
  __do_sys_sendmsg net/socket.c:2689 [inline]
  __se_sys_sendmsg net/socket.c:2687 [inline]
  __x64_sys_sendmsg+0x307/0x4a0 net/socket.c:2687
  x64_sys_call+0x2dd6/0x3c10 arch/x86/include/generated/asm/syscalls_64.h:47
  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

Local variable key created at:
  tcf_ct_flow_table_get+0x4a/0x2260 net/sched/act_ct.c:324
  tcf_ct_init+0xa67/0x2890 net/sched/act_ct.c:1408

Fixes: 88c67ae ("sched: act_ct: add netns into the key of tcf_ct_flow_table")
Reported-by: syzbot+1b5e4e187cc586d05ea0@syzkaller.appspotmail.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Eric Dumazet

net/sched/act_ct.c

@@ -44,6 +44,8 @@ static DEFINE_MUTEX(zones_mutex);
 struct zones_ht_key {
 	struct net *net;
 	u16 zone;
+	/* Note : pad[] must be the last field. */
+	u8  pad[];
 };
 
 struct tcf_ct_flow_table {
@@ -60,7 +62,7 @@ struct tcf_ct_flow_table {
 static const struct rhashtable_params zones_params = {
 	.head_offset = offsetof(struct tcf_ct_flow_table, node),
 	.key_offset = offsetof(struct tcf_ct_flow_table, key),
-	.key_len = sizeof_field(struct tcf_ct_flow_table, key),
+	.key_len = offsetof(struct zones_ht_key, pad),
 	.automatic_shrinking = true,
 };