Alexander Potapenko reported use of uninitialized memory [1]

This happens when inserting a request socket into TCP ehash,
in __sk_nulls_add_node_rcu(), since sk_reuseport is not initialized.

Bug was added by commit d894ba18 ("soreuseport: fix ordering for
mixed v4/v6 sockets")

Note that d296ba60 ("soreuseport: Resolve merge conflict for v4/v6
ordering fix") missed the opportunity to get rid of
hlist_nulls_add_tail_rcu() :

Both UDP sockets and TCP/DCCP listeners no longer use
__sk_nulls_add_node_rcu() for their hash insertion.

Since all other sockets have unique 4-tuple, the reuseport status
has no special meaning, so we can always use hlist_nulls_add_head_rcu()
for them and save few cycles/instructions.

[1]

==================================================================
BUG: KMSAN: use of uninitialized memory in inet_ehash_insert+0xd40/0x1050
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.13.0+ #3288
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:16
 dump_stack+0x185/0x1d0 lib/dump_stack.c:52
 kmsan_report+0x13f/0x1c0 mm/kmsan/kmsan.c:1016
 __msan_warning_32+0x69/0xb0 mm/kmsan/kmsan_instr.c:766
 __sk_nulls_add_node_rcu ./include/net/sock.h:684
 inet_ehash_insert+0xd40/0x1050 net/ipv4/inet_hashtables.c:413
 reqsk_queue_hash_req net/ipv4/inet_connection_sock.c:754
 inet_csk_reqsk_queue_hash_add+0x1cc/0x300 net/ipv4/inet_connection_sock.c:765
 tcp_conn_request+0x31e7/0x36f0 net/ipv4/tcp_input.c:6414
 tcp_v4_conn_request+0x16d/0x220 net/ipv4/tcp_ipv4.c:1314
 tcp_rcv_state_process+0x42a/0x7210 net/ipv4/tcp_input.c:5917
 tcp_v4_do_rcv+0xa6a/0xcd0 net/ipv4/tcp_ipv4.c:1483
 tcp_v4_rcv+0x3de0/0x4ab0 net/ipv4/tcp_ipv4.c:1763
 ip_local_deliver_finish+0x6bb/0xcb0 net/ipv4/ip_input.c:216
 NF_HOOK ./include/linux/netfilter.h:248
 ip_local_deliver+0x3fa/0x480 net/ipv4/ip_input.c:257
 dst_input ./include/net/dst.h:477
 ip_rcv_finish+0x6fb/0x1540 net/ipv4/ip_input.c:397
 NF_HOOK ./include/linux/netfilter.h:248
 ip_rcv+0x10f6/0x15c0 net/ipv4/ip_input.c:488
 __netif_receive_skb_core+0x36f6/0x3f60 net/core/dev.c:4298
 __netif_receive_skb net/core/dev.c:4336
 netif_receive_skb_internal+0x63c/0x19c0 net/core/dev.c:4497
 napi_skb_finish net/core/dev.c:4858
 napi_gro_receive+0x629/0xa50 net/core/dev.c:4889
 e1000_receive_skb drivers/net/ethernet/intel/e1000/e1000_main.c:4018
 e1000_clean_rx_irq+0x1492/0x1d30
drivers/net/ethernet/intel/e1000/e1000_main.c:4474
 e1000_clean+0x43aa/0x5970 drivers/net/ethernet/intel/e1000/e1000_main.c:3819
 napi_poll net/core/dev.c:5500
 net_rx_action+0x73c/0x1820 net/core/dev.c:5566
 __do_softirq+0x4b4/0x8dd kernel/softirq.c:284
 invoke_softirq kernel/softirq.c:364
 irq_exit+0x203/0x240 kernel/softirq.c:405
 exiting_irq+0xe/0x10 ./arch/x86/include/asm/apic.h:638
 do_IRQ+0x15e/0x1a0 arch/x86/kernel/irq.c:263
 common_interrupt+0x86/0x86

Fixes: d894ba18 ("soreuseport: fix ordering for mixed v4/v6 sockets")
Fixes: d296ba60

 ("soreuseport: Resolve merge conflict for v4/v6 ordering fix")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Alexander Potapenko <glider@google.com>
Acked-by: Craig Gallek <kraig@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>