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authorFlorian Westphal <fw@strlen.de>2022-04-25 11:47:11 +0200
committerPablo Neira Ayuso <pablo@netfilter.org>2022-04-27 15:48:45 +0200
commitc7aab4f17021b636a0ee75bcf28e06fb7c94ab48 (patch)
tree015fd364da202646c2e6c28bee5c9b82ad47a10b /net
parenta1bde8c92d27d178a988bfd13d229c170b8135aa (diff)
netfilter: nf_conntrack_tcp: re-init for syn packets only
Jaco Kroon reported tcp problems that Eric Dumazet and Neal Cardwell pinpointed to nf_conntrack tcp_in_window() bug. tcp trace shows following sequence: I > R Flags [S], seq 3451342529, win 62580, options [.. tfo [|tcp]> R > I Flags [S.], seq 2699962254, ack 3451342530, win 65535, options [..] R > I Flags [P.], seq 1:89, ack 1, [..] Note 3rd ACK is from responder to initiator so following branch is taken: } else if (((state->state == TCP_CONNTRACK_SYN_SENT && dir == IP_CT_DIR_ORIGINAL) || (state->state == TCP_CONNTRACK_SYN_RECV && dir == IP_CT_DIR_REPLY)) && after(end, sender->td_end)) { ... because state == TCP_CONNTRACK_SYN_RECV and dir is REPLY. This causes the scaling factor to be reset to 0: window scale option is only present in syn(ack) packets. This in turn makes nf_conntrack mark valid packets as out-of-window. This was always broken, it exists even in original commit where window tracking was added to ip_conntrack (nf_conntrack predecessor) in 2.6.9-rc1 kernel. Restrict to 'tcph->syn', just like the 3rd condtional added in commit 82b72cb94666 ("netfilter: conntrack: re-init state for retransmitted syn-ack"). Upon closer look, those conditionals/branches can be merged: Because earlier checks prevent syn-ack from showing up in original direction, the 'dir' checks in the conditional quoted above are redundant, remove them. Return early for pure syn retransmitted in reply direction (simultaneous open). Fixes: 9fb9cbb1082d ("[NETFILTER]: Add nf_conntrack subsystem.") Reported-by: Jaco Kroon <jaco@uls.co.za> Signed-off-by: Florian Westphal <fw@strlen.de> Acked-by: Jozsef Kadlecsik <kadlec@netfilter.org> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net')
-rw-r--r--net/netfilter/nf_conntrack_proto_tcp.c21
1 files changed, 6 insertions, 15 deletions
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 8ec55cd72572..204a5cdff5b1 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -556,24 +556,14 @@ static bool tcp_in_window(struct nf_conn *ct,
}
}
- } else if (((state->state == TCP_CONNTRACK_SYN_SENT
- && dir == IP_CT_DIR_ORIGINAL)
- || (state->state == TCP_CONNTRACK_SYN_RECV
- && dir == IP_CT_DIR_REPLY))
- && after(end, sender->td_end)) {
+ } else if (tcph->syn &&
+ after(end, sender->td_end) &&
+ (state->state == TCP_CONNTRACK_SYN_SENT ||
+ state->state == TCP_CONNTRACK_SYN_RECV)) {
/*
* RFC 793: "if a TCP is reinitialized ... then it need
* not wait at all; it must only be sure to use sequence
* numbers larger than those recently used."
- */
- sender->td_end =
- sender->td_maxend = end;
- sender->td_maxwin = (win == 0 ? 1 : win);
-
- tcp_options(skb, dataoff, tcph, sender);
- } else if (tcph->syn && dir == IP_CT_DIR_REPLY &&
- state->state == TCP_CONNTRACK_SYN_SENT) {
- /* Retransmitted syn-ack, or syn (simultaneous open).
*
* Re-init state for this direction, just like for the first
* syn(-ack) reply, it might differ in seq, ack or tcp options.
@@ -581,7 +571,8 @@ static bool tcp_in_window(struct nf_conn *ct,
tcp_init_sender(sender, receiver,
skb, dataoff, tcph,
end, win);
- if (!tcph->ack)
+
+ if (dir == IP_CT_DIR_REPLY && !tcph->ack)
return true;
}