Commit b2155e7f70b3f058efe94c0c459db023b05057bd
Committed by
David S. Miller
David S. Miller
1 parent
df922075f2
Exists in
master
and in
7 other branches
[NETFILTER]: nf_conntrack: TCP conntrack reopening fix
TCP connection tracking in netfilter did not handle TCP reopening properly: active close was taken into account for one side only and not for any side, which is fixed now. The patch includes more comments to explain the logic how the different cases are handled. The bug was discovered by Jeff Chua. Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Showing 1 changed file with 26 additions and 6 deletions Side-by-side Diff
net/netfilter/nf_conntrack_proto_tcp.c
| ... | ... | @@ -125,7 +125,7 @@ |
| 125 | 125 | * CLOSE_WAIT: ACK seen (after FIN) |
| 126 | 126 | * LAST_ACK: FIN seen (after FIN) |
| 127 | 127 | * TIME_WAIT: last ACK seen |
| 128 | - * CLOSE: closed connection | |
| 128 | + * CLOSE: closed connection (RST) | |
| 129 | 129 | * |
| 130 | 130 | * LISTEN state is not used. |
| 131 | 131 | * |
| ... | ... | @@ -824,7 +824,21 @@ |
| 824 | 824 | case TCP_CONNTRACK_SYN_SENT: |
| 825 | 825 | if (old_state < TCP_CONNTRACK_TIME_WAIT) |
| 826 | 826 | break; |
| 827 | - if ((ct->proto.tcp.seen[!dir].flags & IP_CT_TCP_FLAG_CLOSE_INIT) | |
| 827 | + /* RFC 1122: "When a connection is closed actively, | |
| 828 | + * it MUST linger in TIME-WAIT state for a time 2xMSL | |
| 829 | + * (Maximum Segment Lifetime). However, it MAY accept | |
| 830 | + * a new SYN from the remote TCP to reopen the connection | |
| 831 | + * directly from TIME-WAIT state, if..." | |
| 832 | + * We ignore the conditions because we are in the | |
| 833 | + * TIME-WAIT state anyway. | |
| 834 | + * | |
| 835 | + * Handle aborted connections: we and the server | |
| 836 | + * think there is an existing connection but the client | |
| 837 | + * aborts it and starts a new one. | |
| 838 | + */ | |
| 839 | + if (((ct->proto.tcp.seen[dir].flags | |
| 840 | + | ct->proto.tcp.seen[!dir].flags) | |
| 841 | + & IP_CT_TCP_FLAG_CLOSE_INIT) | |
| 828 | 842 | || (ct->proto.tcp.last_dir == dir |
| 829 | 843 | && ct->proto.tcp.last_index == TCP_RST_SET)) { |
| 830 | 844 | /* Attempt to reopen a closed/aborted connection. |
| 831 | 845 | |
| 832 | 846 | |
| ... | ... | @@ -838,15 +852,22 @@ |
| 838 | 852 | case TCP_CONNTRACK_IGNORE: |
| 839 | 853 | /* Ignored packets: |
| 840 | 854 | * |
| 855 | + * Our connection entry may be out of sync, so ignore | |
| 856 | + * packets which may signal the real connection between | |
| 857 | + * the client and the server. | |
| 858 | + * | |
| 841 | 859 | * a) SYN in ORIGINAL |
| 842 | 860 | * b) SYN/ACK in REPLY |
| 843 | 861 | * c) ACK in reply direction after initial SYN in original. |
| 862 | + * | |
| 863 | + * If the ignored packet is invalid, the receiver will send | |
| 864 | + * a RST we'll catch below. | |
| 844 | 865 | */ |
| 845 | 866 | if (index == TCP_SYNACK_SET |
| 846 | 867 | && ct->proto.tcp.last_index == TCP_SYN_SET |
| 847 | 868 | && ct->proto.tcp.last_dir != dir |
| 848 | 869 | && ntohl(th->ack_seq) == ct->proto.tcp.last_end) { |
| 849 | - /* This SYN/ACK acknowledges a SYN that we earlier | |
| 870 | + /* b) This SYN/ACK acknowledges a SYN that we earlier | |
| 850 | 871 | * ignored as invalid. This means that the client and |
| 851 | 872 | * the server are both in sync, while the firewall is |
| 852 | 873 | * not. We kill this session and block the SYN/ACK so |
| ... | ... | @@ -870,7 +891,7 @@ |
| 870 | 891 | write_unlock_bh(&tcp_lock); |
| 871 | 892 | if (LOG_INVALID(IPPROTO_TCP)) |
| 872 | 893 | nf_log_packet(pf, 0, skb, NULL, NULL, NULL, |
| 873 | - "nf_ct_tcp: invalid packed ignored "); | |
| 894 | + "nf_ct_tcp: invalid packet ignored "); | |
| 874 | 895 | return NF_ACCEPT; |
| 875 | 896 | case TCP_CONNTRACK_MAX: |
| 876 | 897 | /* Invalid packet */ |
| ... | ... | @@ -924,8 +945,7 @@ |
| 924 | 945 | |
| 925 | 946 | ct->proto.tcp.state = new_state; |
| 926 | 947 | if (old_state != new_state |
| 927 | - && (new_state == TCP_CONNTRACK_FIN_WAIT | |
| 928 | - || new_state == TCP_CONNTRACK_CLOSE)) | |
| 948 | + && new_state == TCP_CONNTRACK_CLOSE) | |
| 929 | 949 | ct->proto.tcp.seen[dir].flags |= IP_CT_TCP_FLAG_CLOSE_INIT; |
| 930 | 950 | timeout = ct->proto.tcp.retrans >= nf_ct_tcp_max_retrans |
| 931 | 951 | && tcp_timeouts[new_state] > nf_ct_tcp_timeout_max_retrans |