tcp/dccp: fix ireq->opt races

syzkaller found another bug in DCCP/TCP stacks [1]

For the reasons explained in commit ce1050089c96 ("tcp/dccp: fix
ireq->pktopts race"), we need to make sure we do not access
ireq->opt unless we own the request sock.

Note the opt field is renamed to ireq_opt to ease grep games.

[1]
BUG: KASAN: use-after-free in ip_queue_xmit+0x1687/0x18e0 net/ipv4/ip_output.c:474
Read of size 1 at addr ffff8801c951039c by task syz-executor5/3295

CPU: 1 PID: 3295 Comm: syz-executor5 Not tainted 4.14.0-rc4+ #80
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:52
print_address_description+0x73/0x250 mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report+0x25b/0x340 mm/kasan/report.c:409
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:427
ip_queue_xmit+0x1687/0x18e0 net/ipv4/ip_output.c:474
tcp_transmit_skb+0x1ab7/0x3840 net/ipv4/tcp_output.c:1135
tcp_send_ack.part.37+0x3bb/0x650 net/ipv4/tcp_output.c:3587
tcp_send_ack+0x49/0x60 net/ipv4/tcp_output.c:3557
__tcp_ack_snd_check+0x2c6/0x4b0 net/ipv4/tcp_input.c:5072
tcp_ack_snd_check net/ipv4/tcp_input.c:5085 [inline]
tcp_rcv_state_process+0x2eff/0x4850 net/ipv4/tcp_input.c:6071
tcp_child_process+0x342/0x990 net/ipv4/tcp_minisocks.c:816
tcp_v4_rcv+0x1827/0x2f80 net/ipv4/tcp_ipv4.c:1682
ip_local_deliver_finish+0x2e2/0xba0 net/ipv4/ip_input.c:216
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_local_deliver+0x1ce/0x6e0 net/ipv4/ip_input.c:257
dst_input include/net/dst.h:464 [inline]
ip_rcv_finish+0x887/0x19a0 net/ipv4/ip_input.c:397
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_rcv+0xc3f/0x1820 net/ipv4/ip_input.c:493
__netif_receive_skb_core+0x1a3e/0x34b0 net/core/dev.c:4476
__netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4514
netif_receive_skb_internal+0x10b/0x670 net/core/dev.c:4587
netif_receive_skb+0xae/0x390 net/core/dev.c:4611
tun_rx_batched.isra.50+0x5ed/0x860 drivers/net/tun.c:1372
tun_get_user+0x249c/0x36d0 drivers/net/tun.c:1766
tun_chr_write_iter+0xbf/0x160 drivers/net/tun.c:1792
call_write_iter include/linux/fs.h:1770 [inline]
new_sync_write fs/read_write.c:468 [inline]
__vfs_write+0x68a/0x970 fs/read_write.c:481
vfs_write+0x18f/0x510 fs/read_write.c:543
SYSC_write fs/read_write.c:588 [inline]
SyS_write+0xef/0x220 fs/read_write.c:580
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x40c341
RSP: 002b:00007f469523ec10 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 000000000040c341
RDX: 0000000000000037 RSI: 0000000020004000 RDI: 0000000000000015
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000f4240 R11: 0000000000000293 R12: 00000000004b7fd1
R13: 00000000ffffffff R14: 0000000020000000 R15: 0000000000025000

Allocated by task 3295:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
__do_kmalloc mm/slab.c:3725 [inline]
__kmalloc+0x162/0x760 mm/slab.c:3734
kmalloc include/linux/slab.h:498 [inline]
tcp_v4_save_options include/net/tcp.h:1962 [inline]
tcp_v4_init_req+0x2d3/0x3e0 net/ipv4/tcp_ipv4.c:1271
tcp_conn_request+0xf6d/0x3410 net/ipv4/tcp_input.c:6283
tcp_v4_conn_request+0x157/0x210 net/ipv4/tcp_ipv4.c:1313
tcp_rcv_state_process+0x8ea/0x4850 net/ipv4/tcp_input.c:5857
tcp_v4_do_rcv+0x55c/0x7d0 net/ipv4/tcp_ipv4.c:1482
tcp_v4_rcv+0x2d10/0x2f80 net/ipv4/tcp_ipv4.c:1711
ip_local_deliver_finish+0x2e2/0xba0 net/ipv4/ip_input.c:216
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_local_deliver+0x1ce/0x6e0 net/ipv4/ip_input.c:257
dst_input include/net/dst.h:464 [inline]
ip_rcv_finish+0x887/0x19a0 net/ipv4/ip_input.c:397
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_rcv+0xc3f/0x1820 net/ipv4/ip_input.c:493
__netif_receive_skb_core+0x1a3e/0x34b0 net/core/dev.c:4476
__netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4514
netif_receive_skb_internal+0x10b/0x670 net/core/dev.c:4587
netif_receive_skb+0xae/0x390 net/core/dev.c:4611
tun_rx_batched.isra.50+0x5ed/0x860 drivers/net/tun.c:1372
tun_get_user+0x249c/0x36d0 drivers/net/tun.c:1766
tun_chr_write_iter+0xbf/0x160 drivers/net/tun.c:1792
call_write_iter include/linux/fs.h:1770 [inline]
new_sync_write fs/read_write.c:468 [inline]
__vfs_write+0x68a/0x970 fs/read_write.c:481
vfs_write+0x18f/0x510 fs/read_write.c:543
SYSC_write fs/read_write.c:588 [inline]
SyS_write+0xef/0x220 fs/read_write.c:580
entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 3306:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3503 [inline]
kfree+0xca/0x250 mm/slab.c:3820
inet_sock_destruct+0x59d/0x950 net/ipv4/af_inet.c:157
__sk_destruct+0xfd/0x910 net/core/sock.c:1560
sk_destruct+0x47/0x80 net/core/sock.c:1595
__sk_free+0x57/0x230 net/core/sock.c:1603
sk_free+0x2a/0x40 net/core/sock.c:1614
sock_put include/net/sock.h:1652 [inline]
inet_csk_complete_hashdance+0xd5/0xf0 net/ipv4/inet_connection_sock.c:959
tcp_check_req+0xf4d/0x1620 net/ipv4/tcp_minisocks.c:765
tcp_v4_rcv+0x17f6/0x2f80 net/ipv4/tcp_ipv4.c:1675
ip_local_deliver_finish+0x2e2/0xba0 net/ipv4/ip_input.c:216
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_local_deliver+0x1ce/0x6e0 net/ipv4/ip_input.c:257
dst_input include/net/dst.h:464 [inline]
ip_rcv_finish+0x887/0x19a0 net/ipv4/ip_input.c:397
NF_HOOK include/linux/netfilter.h:249 [inline]
ip_rcv+0xc3f/0x1820 net/ipv4/ip_input.c:493
__netif_receive_skb_core+0x1a3e/0x34b0 net/core/dev.c:4476
__netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4514
netif_receive_skb_internal+0x10b/0x670 net/core/dev.c:4587
netif_receive_skb+0xae/0x390 net/core/dev.c:4611
tun_rx_batched.isra.50+0x5ed/0x860 drivers/net/tun.c:1372
tun_get_user+0x249c/0x36d0 drivers/net/tun.c:1766
tun_chr_write_iter+0xbf/0x160 drivers/net/tun.c:1792
call_write_iter include/linux/fs.h:1770 [inline]
new_sync_write fs/read_write.c:468 [inline]
__vfs_write+0x68a/0x970 fs/read_write.c:481
vfs_write+0x18f/0x510 fs/read_write.c:543
SYSC_write fs/read_write.c:588 [inline]
SyS_write+0xef/0x220 fs/read_write.c:580
entry_SYSCALL_64_fastpath+0x1f/0xbe

Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/inet_sock.h

···
 	kmemcheck_bitfield_end(flags);
 	u32                     ir_mark;
 	union {
-		struct ip_options_rcu	*opt;
+		struct ip_options_rcu __rcu	*ireq_opt;
 #if IS_ENABLED(CONFIG_IPV6)
 		struct {
 			struct ipv6_txoptions	*ipv6_opt;

net/dccp/ipv4.c

···
 	sk_daddr_set(newsk, ireq->ir_rmt_addr);
 	sk_rcv_saddr_set(newsk, ireq->ir_loc_addr);
 	newinet->inet_saddr	= ireq->ir_loc_addr;
-	newinet->inet_opt	= ireq->opt;
-	ireq->opt	   = NULL;
+	RCU_INIT_POINTER(newinet->inet_opt, rcu_dereference(ireq->ireq_opt));
 	newinet->mc_index  = inet_iif(skb);
 	newinet->mc_ttl	   = ip_hdr(skb)->ttl;
 	newinet->inet_id   = jiffies;
···
 	if (__inet_inherit_port(sk, newsk) < 0)
 		goto put_and_exit;
 	*own_req = inet_ehash_nolisten(newsk, req_to_sk(req_unhash));
-
+	if (*own_req)
+		ireq->ireq_opt = NULL;
+	else
+		newinet->inet_opt = NULL;
 	return newsk;
 
 exit_overflow:
···
 	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENDROPS);
 	return NULL;
 put_and_exit:
+	newinet->inet_opt = NULL;
 	inet_csk_prepare_forced_close(newsk);
 	dccp_done(newsk);
 	goto exit;
···
 							      ireq->ir_rmt_addr);
 		err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr,
 					    ireq->ir_rmt_addr,
-					    ireq->opt);
+					    rcu_dereference(ireq->ireq_opt));
 		err = net_xmit_eval(err);
 	}
 
···
 static void dccp_v4_reqsk_destructor(struct request_sock *req)
 {
 	dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg);
-	kfree(inet_rsk(req)->opt);
+	kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1));
 }
 
 void dccp_syn_ack_timeout(const struct request_sock *req)

net/ipv4/cipso_ipv4.c

···
 	buf = NULL;
 
 	req_inet = inet_rsk(req);
-	opt = xchg(&req_inet->opt, opt);
+	opt = xchg((__force struct ip_options_rcu **)&req_inet->ireq_opt, opt);
 	if (opt)
 		kfree_rcu(opt, rcu);
 
···
  * values on failure.
  *
  */
-static int cipso_v4_delopt(struct ip_options_rcu **opt_ptr)
+static int cipso_v4_delopt(struct ip_options_rcu __rcu **opt_ptr)
 {
+	struct ip_options_rcu *opt = rcu_dereference_protected(*opt_ptr, 1);
 	int hdr_delta = 0;
-	struct ip_options_rcu *opt = *opt_ptr;
 
+	if (!opt || opt->opt.cipso == 0)
+		return 0;
 	if (opt->opt.srr || opt->opt.rr || opt->opt.ts || opt->opt.router_alert) {
 		u8 cipso_len;
 		u8 cipso_off;
···
  */
 void cipso_v4_sock_delattr(struct sock *sk)
 {
-	int hdr_delta;
-	struct ip_options_rcu *opt;
 	struct inet_sock *sk_inet;
+	int hdr_delta;
 
 	sk_inet = inet_sk(sk);
-	opt = rcu_dereference_protected(sk_inet->inet_opt, 1);
-	if (!opt || opt->opt.cipso == 0)
-		return;
 
 	hdr_delta = cipso_v4_delopt(&sk_inet->inet_opt);
 	if (sk_inet->is_icsk && hdr_delta > 0) {
···
  */
 void cipso_v4_req_delattr(struct request_sock *req)
 {
-	struct ip_options_rcu *opt;
-	struct inet_request_sock *req_inet;
-
-	req_inet = inet_rsk(req);
-	opt = req_inet->opt;
-	if (!opt || opt->opt.cipso == 0)
-		return;
-
-	cipso_v4_delopt(&req_inet->opt);
+	cipso_v4_delopt(&inet_rsk(req)->ireq_opt);
 }
 
 /**

net/ipv4/inet_connection_sock.c

···
 {
 	const struct inet_request_sock *ireq = inet_rsk(req);
 	struct net *net = read_pnet(&ireq->ireq_net);
-	struct ip_options_rcu *opt = ireq->opt;
+	struct ip_options_rcu *opt;
 	struct rtable *rt;
 
+	opt = rcu_dereference(ireq->ireq_opt);
 	flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
 			   RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
 			   sk->sk_protocol, inet_sk_flowi_flags(sk),
···
 	struct flowi4 *fl4;
 	struct rtable *rt;
 
+	opt = rcu_dereference(ireq->ireq_opt);
 	fl4 = &newinet->cork.fl.u.ip4;
 
-	rcu_read_lock();
-	opt = rcu_dereference(newinet->inet_opt);
 	flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
 			   RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
 			   sk->sk_protocol, inet_sk_flowi_flags(sk),
···
 		goto no_route;
 	if (opt && opt->opt.is_strictroute && rt->rt_uses_gateway)
 		goto route_err;
-	rcu_read_unlock();
 	return &rt->dst;
 
 route_err:
 	ip_rt_put(rt);
 no_route:
-	rcu_read_unlock();
 	__IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
 	return NULL;
 }

net/ipv4/syncookies.c

···
 	/* We throwed the options of the initial SYN away, so we hope
 	 * the ACK carries the same options again (see RFC1122 4.2.3.8)
 	 */
-	ireq->opt = tcp_v4_save_options(sock_net(sk), skb);
+	RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(sock_net(sk), skb));
 
 	if (security_inet_conn_request(sk, skb, req)) {
 		reqsk_free(req);

net/ipv4/tcp_input.c

···
 		struct inet_request_sock *ireq = inet_rsk(req);
 
 		kmemcheck_annotate_bitfield(ireq, flags);
-		ireq->opt = NULL;
+		ireq->ireq_opt = NULL;
 #if IS_ENABLED(CONFIG_IPV6)
 		ireq->pktopts = NULL;
 #endif

net/ipv4/tcp_ipv4.c

···
 
 		err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr,
 					    ireq->ir_rmt_addr,
-					    ireq->opt);
+					    rcu_dereference(ireq->ireq_opt));
 		err = net_xmit_eval(err);
 	}
 
···
  */
 static void tcp_v4_reqsk_destructor(struct request_sock *req)
 {
-	kfree(inet_rsk(req)->opt);
+	kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1));
 }
 
 #ifdef CONFIG_TCP_MD5SIG
···
 			    struct sk_buff *skb)
 {
 	struct inet_request_sock *ireq = inet_rsk(req);
+	struct net *net = sock_net(sk_listener);
 
 	sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
 	sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
-	ireq->opt = tcp_v4_save_options(sock_net(sk_listener), skb);
+	RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(net, skb));
 }
 
 static struct dst_entry *tcp_v4_route_req(const struct sock *sk,
···
 	sk_daddr_set(newsk, ireq->ir_rmt_addr);
 	sk_rcv_saddr_set(newsk, ireq->ir_loc_addr);
 	newsk->sk_bound_dev_if = ireq->ir_iif;
-	newinet->inet_saddr	      = ireq->ir_loc_addr;
-	inet_opt	      = ireq->opt;
-	rcu_assign_pointer(newinet->inet_opt, inet_opt);
-	ireq->opt	      = NULL;
+	newinet->inet_saddr   = ireq->ir_loc_addr;
+	inet_opt	      = rcu_dereference(ireq->ireq_opt);
+	RCU_INIT_POINTER(newinet->inet_opt, inet_opt);
 	newinet->mc_index     = inet_iif(skb);
 	newinet->mc_ttl	      = ip_hdr(skb)->ttl;
 	newinet->rcv_tos      = ip_hdr(skb)->tos;
···
 	if (__inet_inherit_port(sk, newsk) < 0)
 		goto put_and_exit;
 	*own_req = inet_ehash_nolisten(newsk, req_to_sk(req_unhash));
-	if (*own_req)
+	if (likely(*own_req)) {
 		tcp_move_syn(newtp, req);
-
+		ireq->ireq_opt = NULL;
+	} else {
+		newinet->inet_opt = NULL;
+	}
 	return newsk;
 
 exit_overflow:
···
 	tcp_listendrop(sk);
 	return NULL;
 put_and_exit:
+	newinet->inet_opt = NULL;
 	inet_csk_prepare_forced_close(newsk);
 	tcp_done(newsk);
 	goto exit;