netfilter: conntrack: annotate data-races around ct->timeout

(struct nf_conn)->timeout can be read/written locklessly,
add READ_ONCE()/WRITE_ONCE() to prevent load/store tearing.

BUG: KCSAN: data-race in __nf_conntrack_alloc / __nf_conntrack_find_get

write to 0xffff888132e78c08 of 4 bytes by task 6029 on cpu 0:
__nf_conntrack_alloc+0x158/0x280 net/netfilter/nf_conntrack_core.c:1563
init_conntrack+0x1da/0xb30 net/netfilter/nf_conntrack_core.c:1635
resolve_normal_ct+0x502/0x610 net/netfilter/nf_conntrack_core.c:1746
nf_conntrack_in+0x1c5/0x88f net/netfilter/nf_conntrack_core.c:1901
ipv6_conntrack_local+0x19/0x20 net/netfilter/nf_conntrack_proto.c:414
nf_hook_entry_hookfn include/linux/netfilter.h:142 [inline]
nf_hook_slow+0x72/0x170 net/netfilter/core.c:619
nf_hook include/linux/netfilter.h:262 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ip6_xmit+0xa3a/0xa60 net/ipv6/ip6_output.c:324
inet6_csk_xmit+0x1a2/0x1e0 net/ipv6/inet6_connection_sock.c:135
__tcp_transmit_skb+0x132a/0x1840 net/ipv4/tcp_output.c:1402
tcp_transmit_skb net/ipv4/tcp_output.c:1420 [inline]
tcp_write_xmit+0x1450/0x4460 net/ipv4/tcp_output.c:2680
__tcp_push_pending_frames+0x68/0x1c0 net/ipv4/tcp_output.c:2864
tcp_push_pending_frames include/net/tcp.h:1897 [inline]
tcp_data_snd_check+0x62/0x2e0 net/ipv4/tcp_input.c:5452
tcp_rcv_established+0x880/0x10e0 net/ipv4/tcp_input.c:5947
tcp_v6_do_rcv+0x36e/0xa50 net/ipv6/tcp_ipv6.c:1521
sk_backlog_rcv include/net/sock.h:1030 [inline]
__release_sock+0xf2/0x270 net/core/sock.c:2768
release_sock+0x40/0x110 net/core/sock.c:3300
sk_stream_wait_memory+0x435/0x700 net/core/stream.c:145
tcp_sendmsg_locked+0xb85/0x25a0 net/ipv4/tcp.c:1402
tcp_sendmsg+0x2c/0x40 net/ipv4/tcp.c:1440
inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:644
sock_sendmsg_nosec net/socket.c:704 [inline]
sock_sendmsg net/socket.c:724 [inline]
__sys_sendto+0x21e/0x2c0 net/socket.c:2036
__do_sys_sendto net/socket.c:2048 [inline]
__se_sys_sendto net/socket.c:2044 [inline]
__x64_sys_sendto+0x74/0x90 net/socket.c:2044
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888132e78c08 of 4 bytes by task 17446 on cpu 1:
nf_ct_is_expired include/net/netfilter/nf_conntrack.h:286 [inline]
____nf_conntrack_find net/netfilter/nf_conntrack_core.c:776 [inline]
__nf_conntrack_find_get+0x1c7/0xac0 net/netfilter/nf_conntrack_core.c:807
resolve_normal_ct+0x273/0x610 net/netfilter/nf_conntrack_core.c:1734
nf_conntrack_in+0x1c5/0x88f net/netfilter/nf_conntrack_core.c:1901
ipv6_conntrack_local+0x19/0x20 net/netfilter/nf_conntrack_proto.c:414
nf_hook_entry_hookfn include/linux/netfilter.h:142 [inline]
nf_hook_slow+0x72/0x170 net/netfilter/core.c:619
nf_hook include/linux/netfilter.h:262 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ip6_xmit+0xa3a/0xa60 net/ipv6/ip6_output.c:324
inet6_csk_xmit+0x1a2/0x1e0 net/ipv6/inet6_connection_sock.c:135
__tcp_transmit_skb+0x132a/0x1840 net/ipv4/tcp_output.c:1402
__tcp_send_ack+0x1fd/0x300 net/ipv4/tcp_output.c:3956
tcp_send_ack+0x23/0x30 net/ipv4/tcp_output.c:3962
__tcp_ack_snd_check+0x2d8/0x510 net/ipv4/tcp_input.c:5478
tcp_ack_snd_check net/ipv4/tcp_input.c:5523 [inline]
tcp_rcv_established+0x8c2/0x10e0 net/ipv4/tcp_input.c:5948
tcp_v6_do_rcv+0x36e/0xa50 net/ipv6/tcp_ipv6.c:1521
sk_backlog_rcv include/net/sock.h:1030 [inline]
__release_sock+0xf2/0x270 net/core/sock.c:2768
release_sock+0x40/0x110 net/core/sock.c:3300
tcp_sendpage+0x94/0xb0 net/ipv4/tcp.c:1114
inet_sendpage+0x7f/0xc0 net/ipv4/af_inet.c:833
rds_tcp_xmit+0x376/0x5f0 net/rds/tcp_send.c:118
rds_send_xmit+0xbed/0x1500 net/rds/send.c:367
rds_send_worker+0x43/0x200 net/rds/threads.c:200
process_one_work+0x3fc/0x980 kernel/workqueue.c:2298
worker_thread+0x616/0xa70 kernel/workqueue.c:2445
kthread+0x2c7/0x2e0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30

value changed: 0x00027cc2 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17446 Comm: kworker/u4:5 Tainted: G W 5.16.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: krdsd rds_send_worker

Note: I chose an arbitrary commit for the Fixes: tag,
because I do not think we need to backport this fix to very old kernels.

Fixes: e37542ba111f ("netfilter: conntrack: avoid possible false sharing")
Signed-off-by: Eric Dumazet <[e-mail]>
Reported-by: syzbot <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/net/netfilter/nf_conntrack.h

···
 /* jiffies until ct expires, 0 if already expired */
 static inline unsigned long nf_ct_expires(const struct nf_conn *ct)
 {
-	s32 timeout = ct->timeout - nfct_time_stamp;
+	s32 timeout = READ_ONCE(ct->timeout) - nfct_time_stamp;
 
 	return timeout > 0 ? timeout : 0;
 }
 
 static inline bool nf_ct_is_expired(const struct nf_conn *ct)
 {
-	return (__s32)(ct->timeout - nfct_time_stamp) <= 0;
+	return (__s32)(READ_ONCE(ct->timeout) - nfct_time_stamp) <= 0;
 }
 
 /* use after obtaining a reference count */
···
 static inline void nf_ct_offload_timeout(struct nf_conn *ct)
 {
 	if (nf_ct_expires(ct) < NF_CT_DAY / 2)
-		ct->timeout = nfct_time_stamp + NF_CT_DAY;
+		WRITE_ONCE(ct->timeout, nfct_time_stamp + NF_CT_DAY);
 }
 
 struct kernel_param;

net/netfilter/nf_conntrack_core.c

···
 
 	tstamp = nf_conn_tstamp_find(ct);
 	if (tstamp) {
-		s32 timeout = ct->timeout - nfct_time_stamp;
+		s32 timeout = READ_ONCE(ct->timeout) - nfct_time_stamp;
 
 		tstamp->stop = ktime_get_real_ns();
 		if (timeout < 0)
···
 	}
 
 	/* We want the clashing entry to go away real soon: 1 second timeout. */
-	loser_ct->timeout = nfct_time_stamp + HZ;
+	WRITE_ONCE(loser_ct->timeout, nfct_time_stamp + HZ);
 
 	/* IPS_NAT_CLASH removes the entry automatically on the first
 	 * reply.  Also prevents UDP tracker from moving the entry to
···
 	/* save hash for reusing when confirming */
 	*(unsigned long *)(&ct->tuplehash[IP_CT_DIR_REPLY].hnnode.pprev) = hash;
 	ct->status = 0;
-	ct->timeout = 0;
+	WRITE_ONCE(ct->timeout, 0);
 	write_pnet(&ct->ct_net, net);
 	memset(&ct->__nfct_init_offset, 0,
 	       offsetof(struct nf_conn, proto) -

net/netfilter/nf_conntrack_netlink.c

···
 
 	if (timeout > INT_MAX)
 		timeout = INT_MAX;
-	ct->timeout = nfct_time_stamp + (u32)timeout;
+	WRITE_ONCE(ct->timeout, nfct_time_stamp + (u32)timeout);
 
 	if (test_bit(IPS_DYING_BIT, &ct->status))
 		return -ETIME;

net/netfilter/nf_flow_table_core.c

···
 	if (timeout < 0)
 		timeout = 0;
 
-	if (nf_flow_timeout_delta(ct->timeout) > (__s32)timeout)
-		ct->timeout = nfct_time_stamp + timeout;
+	if (nf_flow_timeout_delta(READ_ONCE(ct->timeout)) > (__s32)timeout)
+		WRITE_ONCE(ct->timeout, nfct_time_stamp + timeout);
 }
 
 static void flow_offload_fixup_ct_state(struct nf_conn *ct)