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 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

Uninit was stored to memory at:
  nf_reject_ip6_tcphdr_put+0x2ca/0x6c0 net/ipv6/netfilter/nf_reject_ipv6.c:231
  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

Uninit was created at:
  slab_post_alloc_hook mm/slub.c:3998 [inline]
  slab_alloc_node mm/slub.c:4041 [inline]
  kmem_cache_alloc_node_noprof+0x6bf/0xb80 mm/slub.c:4084
  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:583
  __alloc_skb+0x363/0x7b0 net/core/skbuff.c:674
  alloc_skb include/linux/skbuff.h:1320 [inline]
  nf_send_reset6+0x98d/0x15b0 net/ipv6/netfilter/nf_reject_ipv6.c:327
  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

Fixes: c8d7b98 ("netfilter: move nf_send_resetX() code to nf_reject_ipvX modules")
Reported-by: syzbot <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Reviewed-by: Pablo Neira Ayuso <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: edumazet

net/ipv6/netfilter/nf_reject_ipv6.c

@@ -223,33 +223,23 @@ void nf_reject_ip6_tcphdr_put(struct sk_buff *nskb,
 			      const struct tcphdr *oth, unsigned int otcplen)
 {
 	struct tcphdr *tcph;
-	int needs_ack;
 
 	skb_reset_transport_header(nskb);
-	tcph = skb_put(nskb, sizeof(struct tcphdr));
+	tcph = skb_put_zero(nskb, sizeof(struct tcphdr));
 	/* Truncate to length (no data) */
 	tcph->doff = sizeof(struct tcphdr)/4;
 	tcph->source = oth->dest;
 	tcph->dest = oth->source;
 
 	if (oth->ack) {
-		needs_ack = 0;
 		tcph->seq = oth->ack_seq;
-		tcph->ack_seq = 0;
 	} else {
-		needs_ack = 1;
 		tcph->ack_seq = htonl(ntohl(oth->seq) + oth->syn + oth->fin +
 				      otcplen - (oth->doff<<2));
-		tcph->seq = 0;
+		tcph->ack = 1;
 	}
 
-	/* Reset flags */
-	((u_int8_t *)tcph)[13] = 0;
 	tcph->rst = 1;
-	tcph->ack = needs_ack;
-	tcph->window = 0;
-	tcph->urg_ptr = 0;
-	tcph->check = 0;
 
 	/* Adjust TCP checksum */
 	tcph->check = csum_ipv6_magic(&ipv6_hdr(nskb)->saddr,