From bfcaa50270e18f35220a11d46e98fc6232c24606 Mon Sep 17 00:00:00 2001 From: Jozsef Kadlecsik Date: Mon, 25 May 2009 17:23:15 +0200 Subject: [PATCH 1/4] netfilter: nf_ct_tcp: fix accepting invalid RST segments Robert L Mathews discovered that some clients send evil TCP RST segments, which are accepted by netfilter conntrack but discarded by the destination. Thus the conntrack entry is destroyed but the destination retransmits data until timeout. The same technique, i.e. sending properly crafted RST segments, can easily be used to bypass connlimit/connbytes based restrictions (the sample script written by Robert can be found in the netfilter mailing list archives). The patch below adds a new flag and new field to struct ip_ct_tcp_state so that checking RST segments can be made more strict and thus TCP conntrack can catch the invalid ones: the RST segment is accepted only if its sequence number higher than or equal to the highest ack we seen from the other direction. (The last_ack field cannot be reused because it is used to catch resent packets.) Signed-off-by: Jozsef Kadlecsik Signed-off-by: Patrick McHardy --- include/linux/netfilter/nf_conntrack_tcp.h | 4 ++++ net/netfilter/nf_conntrack_proto_tcp.c | 18 ++++++++++++++++++ 2 files changed, 22 insertions(+) diff --git a/include/linux/netfilter/nf_conntrack_tcp.h b/include/linux/netfilter/nf_conntrack_tcp.h index 3066789b972a..b2f384d42611 100644 --- a/include/linux/netfilter/nf_conntrack_tcp.h +++ b/include/linux/netfilter/nf_conntrack_tcp.h @@ -35,6 +35,9 @@ enum tcp_conntrack { /* Has unacknowledged data */ #define IP_CT_TCP_FLAG_DATA_UNACKNOWLEDGED 0x10 +/* The field td_maxack has been set */ +#define IP_CT_TCP_FLAG_MAXACK_SET 0x20 + struct nf_ct_tcp_flags { __u8 flags; __u8 mask; @@ -46,6 +49,7 @@ struct ip_ct_tcp_state { u_int32_t td_end; /* max of seq + len */ u_int32_t td_maxend; /* max of ack + max(win, 1) */ u_int32_t td_maxwin; /* max(win) */ + u_int32_t td_maxack; /* max of ack */ u_int8_t td_scale; /* window scale factor */ u_int8_t flags; /* per direction options */ }; diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index b5ccf2b4b2e7..97a6e93d742e 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -634,6 +634,14 @@ static bool tcp_in_window(const struct nf_conn *ct, sender->td_end = end; sender->flags |= IP_CT_TCP_FLAG_DATA_UNACKNOWLEDGED; } + if (tcph->ack) { + if (!(sender->flags & IP_CT_TCP_FLAG_MAXACK_SET)) { + sender->td_maxack = ack; + sender->flags |= IP_CT_TCP_FLAG_MAXACK_SET; + } else if (after(ack, sender->td_maxack)) + sender->td_maxack = ack; + } + /* * Update receiver data. */ @@ -918,6 +926,16 @@ static int tcp_packet(struct nf_conn *ct, "nf_ct_tcp: invalid state "); return -NF_ACCEPT; case TCP_CONNTRACK_CLOSE: + if (index == TCP_RST_SET + && (ct->proto.tcp.seen[!dir].flags & IP_CT_TCP_FLAG_MAXACK_SET) + && before(ntohl(th->seq), ct->proto.tcp.seen[!dir].td_maxack)) { + /* Invalid RST */ + write_unlock_bh(&tcp_lock); + if (LOG_INVALID(net, IPPROTO_TCP)) + nf_log_packet(pf, 0, skb, NULL, NULL, NULL, + "nf_ct_tcp: invalid RST "); + return -NF_ACCEPT; + } if (index == TCP_RST_SET && ((test_bit(IPS_SEEN_REPLY_BIT, &ct->status) && ct->proto.tcp.last_index == TCP_SYN_SET) From b38b1f616867c832301f24eaf259889494d495b3 Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Mon, 25 May 2009 17:29:43 +0200 Subject: [PATCH 2/4] netfilter: nf_ct_dccp: add missing DCCP protocol changes in event cache This patch adds the missing protocol state-change event reporting for DCCP. $ sudo conntrack -E [NEW] dccp 33 240 src=192.168.0.2 dst=192.168.1.2 sport=57040 dport=5001 [UNREPLIED] src=192.168.1.2 dst=192.168.1.100 sport=5001 dport=57040 With this patch: $ sudo conntrack -E [NEW] dccp 33 240 REQUEST src=192.168.0.2 dst=192.168.1.2 sport=57040 dport=5001 [UNREPLIED] src=192.168.1.2 dst=192.168.1.100 sport=5001 dport=57040 Signed-off-by: Pablo Neira Ayuso Signed-off-by: Patrick McHardy --- net/netfilter/nf_conntrack_proto_dccp.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/netfilter/nf_conntrack_proto_dccp.c b/net/netfilter/nf_conntrack_proto_dccp.c index 8e757dd53396..aee0d6bea309 100644 --- a/net/netfilter/nf_conntrack_proto_dccp.c +++ b/net/netfilter/nf_conntrack_proto_dccp.c @@ -22,6 +22,7 @@ #include #include #include +#include #include static DEFINE_RWLOCK(dccp_lock); @@ -553,6 +554,9 @@ static int dccp_packet(struct nf_conn *ct, const struct sk_buff *skb, ct->proto.dccp.state = new_state; write_unlock_bh(&dccp_lock); + if (new_state != old_state) + nf_conntrack_event_cache(IPCT_PROTOINFO, ct); + dn = dccp_pernet(net); nf_ct_refresh_acct(ct, ctinfo, skb, dn->dccp_timeout[new_state]); From 683a04cebc63819a36b1db19843bd17771f05b55 Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Wed, 27 May 2009 15:45:34 +0200 Subject: [PATCH 3/4] netfilter: xt_hashlimit does a wrong SEQ_SKIP The function dl_seq_show() returns 1 (equal to SEQ_SKIP) in case a seq_printf() call return -1. It should return -1. This SEQ_SKIP behavior brakes processing the proc file e.g. via a pipe or just through less. Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Patrick McHardy --- net/netfilter/xt_hashlimit.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c index a5b5369c30f9..219dcdbe388c 100644 --- a/net/netfilter/xt_hashlimit.c +++ b/net/netfilter/xt_hashlimit.c @@ -926,7 +926,7 @@ static int dl_seq_show(struct seq_file *s, void *v) if (!hlist_empty(&htable->hash[*bucket])) { hlist_for_each_entry(ent, pos, &htable->hash[*bucket], node) if (dl_seq_real_show(ent, htable->family, s)) - return 1; + return -1; } return 0; } From eeff9beec3d2563c42cca41e66d4169592bb5475 Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Wed, 27 May 2009 15:49:11 +0200 Subject: [PATCH 4/4] netfilter: nfnetlink_log: fix wrong skbuff size calculation This problem was introduced in 72961ecf84d67d6359a1b30f9b2a8427f13e1e71 since no space was reserved for the new attributes NFULA_HWTYPE, NFULA_HWLEN and NFULA_HWHEADER. Signed-off-by: Pablo Neira Ayuso Signed-off-by: Patrick McHardy --- net/netfilter/nfnetlink_log.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c index fd326ac27ec8..66a6dd5c519a 100644 --- a/net/netfilter/nfnetlink_log.c +++ b/net/netfilter/nfnetlink_log.c @@ -581,6 +581,12 @@ nfulnl_log_packet(u_int8_t pf, + nla_total_size(sizeof(struct nfulnl_msg_packet_hw)) + nla_total_size(sizeof(struct nfulnl_msg_packet_timestamp)); + if (in && skb_mac_header_was_set(skb)) { + size += nla_total_size(skb->dev->hard_header_len) + + nla_total_size(sizeof(u_int16_t)) /* hwtype */ + + nla_total_size(sizeof(u_int16_t)); /* hwlen */ + } + spin_lock_bh(&inst->lock); if (inst->flags & NFULNL_CFG_F_SEQ)