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netfilter: nf_nat: fix NAT issue in 2.6.30.4+
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Vitezslav Samel discovered that since 2.6.30.4+ active FTP can not work
over NAT. The "cause" of the problem was a fix of unacknowledged data
detection with NAT (commit a3a9f79).
However, actually, that fix uncovered a long standing bug in TCP conntrack:
when NAT was enabled, we simply updated the max of the right edge of
the segments we have seen (td_end), by the offset NAT produced with
changing IP/port in the data. However, we did not update the other parameter
(td_maxend) which is affected by the NAT offset. Thus that could drift
away from the correct value and thus resulted breaking active FTP.

The patch below fixes the issue by *not* updating the conntrack parameters
from NAT, but instead taking into account the NAT offsets in conntrack in a
consistent way. (Updating from NAT would be more harder and expensive because
it'd need to re-calculate parameters we already calculated in conntrack.)

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>
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Jozsef Kadlecsik authored and David S. Miller committed Nov 6, 2009
1 parent f5209b4 commit f9dd09c
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Showing 6 changed files with 67 additions and 54 deletions.
8 changes: 3 additions & 5 deletions include/net/netfilter/nf_conntrack.h
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Original file line number Diff line number Diff line change
Expand Up @@ -255,11 +255,9 @@ static inline bool nf_ct_kill(struct nf_conn *ct)
}

/* These are for NAT. Icky. */
/* Update TCP window tracking data when NAT mangles the packet */
extern void nf_conntrack_tcp_update(const struct sk_buff *skb,
unsigned int dataoff,
struct nf_conn *ct, int dir,
s16 offset);
extern s16 (*nf_ct_nat_offset)(const struct nf_conn *ct,
enum ip_conntrack_dir dir,
u32 seq);

/* Fake conntrack entry for untracked connections */
extern struct nf_conn nf_conntrack_untracked;
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4 changes: 4 additions & 0 deletions include/net/netfilter/nf_nat_helper.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,4 +32,8 @@ extern int (*nf_nat_seq_adjust_hook)(struct sk_buff *skb,
* to port ct->master->saved_proto. */
extern void nf_nat_follow_master(struct nf_conn *ct,
struct nf_conntrack_expect *this);

extern s16 nf_nat_get_offset(const struct nf_conn *ct,
enum ip_conntrack_dir dir,
u32 seq);
#endif
3 changes: 3 additions & 0 deletions net/ipv4/netfilter/nf_nat_core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -750,6 +750,8 @@ static int __init nf_nat_init(void)
BUG_ON(nfnetlink_parse_nat_setup_hook != NULL);
rcu_assign_pointer(nfnetlink_parse_nat_setup_hook,
nfnetlink_parse_nat_setup);
BUG_ON(nf_ct_nat_offset != NULL);
rcu_assign_pointer(nf_ct_nat_offset, nf_nat_get_offset);
return 0;

cleanup_extend:
Expand All @@ -764,6 +766,7 @@ static void __exit nf_nat_cleanup(void)
nf_ct_extend_unregister(&nat_extend);
rcu_assign_pointer(nf_nat_seq_adjust_hook, NULL);
rcu_assign_pointer(nfnetlink_parse_nat_setup_hook, NULL);
rcu_assign_pointer(nf_ct_nat_offset, NULL);
synchronize_net();
}

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34 changes: 23 additions & 11 deletions net/ipv4/netfilter/nf_nat_helper.c
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,28 @@ adjust_tcp_sequence(u32 seq,
DUMP_OFFSET(this_way);
}

/* Get the offset value, for conntrack */
s16 nf_nat_get_offset(const struct nf_conn *ct,
enum ip_conntrack_dir dir,
u32 seq)
{
struct nf_conn_nat *nat = nfct_nat(ct);
struct nf_nat_seq *this_way;
s16 offset;

if (!nat)
return 0;

this_way = &nat->seq[dir];
spin_lock_bh(&nf_nat_seqofs_lock);
offset = after(seq, this_way->correction_pos)
? this_way->offset_after : this_way->offset_before;
spin_unlock_bh(&nf_nat_seqofs_lock);

return offset;
}
EXPORT_SYMBOL_GPL(nf_nat_get_offset);

/* Frobs data inside this packet, which is linear. */
static void mangle_contents(struct sk_buff *skb,
unsigned int dataoff,
Expand Down Expand Up @@ -189,11 +211,6 @@ nf_nat_mangle_tcp_packet(struct sk_buff *skb,
adjust_tcp_sequence(ntohl(tcph->seq),
(int)rep_len - (int)match_len,
ct, ctinfo);
/* Tell TCP window tracking about seq change */
nf_conntrack_tcp_update(skb, ip_hdrlen(skb),
ct, CTINFO2DIR(ctinfo),
(int)rep_len - (int)match_len);

nf_conntrack_event_cache(IPCT_NATSEQADJ, ct);
}
return 1;
Expand Down Expand Up @@ -415,12 +432,7 @@ nf_nat_seq_adjust(struct sk_buff *skb,
tcph->seq = newseq;
tcph->ack_seq = newack;

if (!nf_nat_sack_adjust(skb, tcph, ct, ctinfo))
return 0;

nf_conntrack_tcp_update(skb, ip_hdrlen(skb), ct, dir, seqoff);

return 1;
return nf_nat_sack_adjust(skb, tcph, ct, ctinfo);
}

/* Setup NAT on this expected conntrack so it follows master. */
Expand Down
8 changes: 8 additions & 0 deletions net/netfilter/nf_conntrack_core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1350,6 +1350,11 @@ static int nf_conntrack_init_net(struct net *net)
return ret;
}

s16 (*nf_ct_nat_offset)(const struct nf_conn *ct,
enum ip_conntrack_dir dir,
u32 seq);
EXPORT_SYMBOL_GPL(nf_ct_nat_offset);

int nf_conntrack_init(struct net *net)
{
int ret;
Expand All @@ -1367,6 +1372,9 @@ int nf_conntrack_init(struct net *net)
/* For use by REJECT target */
rcu_assign_pointer(ip_ct_attach, nf_conntrack_attach);
rcu_assign_pointer(nf_ct_destroy, destroy_conntrack);

/* Howto get NAT offsets */
rcu_assign_pointer(nf_ct_nat_offset, NULL);
}
return 0;

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64 changes: 26 additions & 38 deletions net/netfilter/nf_conntrack_proto_tcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -492,6 +492,21 @@ static void tcp_sack(const struct sk_buff *skb, unsigned int dataoff,
}
}

#ifdef CONFIG_NF_NAT_NEEDED
static inline s16 nat_offset(const struct nf_conn *ct,
enum ip_conntrack_dir dir,
u32 seq)
{
typeof(nf_ct_nat_offset) get_offset = rcu_dereference(nf_ct_nat_offset);

return get_offset != NULL ? get_offset(ct, dir, seq) : 0;
}
#define NAT_OFFSET(pf, ct, dir, seq) \
(pf == NFPROTO_IPV4 ? nat_offset(ct, dir, seq) : 0)
#else
#define NAT_OFFSET(pf, ct, dir, seq) 0
#endif

static bool tcp_in_window(const struct nf_conn *ct,
struct ip_ct_tcp *state,
enum ip_conntrack_dir dir,
Expand All @@ -506,6 +521,7 @@ static bool tcp_in_window(const struct nf_conn *ct,
struct ip_ct_tcp_state *receiver = &state->seen[!dir];
const struct nf_conntrack_tuple *tuple = &ct->tuplehash[dir].tuple;
__u32 seq, ack, sack, end, win, swin;
s16 receiver_offset;
bool res;

/*
Expand All @@ -519,11 +535,16 @@ static bool tcp_in_window(const struct nf_conn *ct,
if (receiver->flags & IP_CT_TCP_FLAG_SACK_PERM)
tcp_sack(skb, dataoff, tcph, &sack);

/* Take into account NAT sequence number mangling */
receiver_offset = NAT_OFFSET(pf, ct, !dir, ack - 1);
ack -= receiver_offset;
sack -= receiver_offset;

pr_debug("tcp_in_window: START\n");
pr_debug("tcp_in_window: ");
nf_ct_dump_tuple(tuple);
pr_debug("seq=%u ack=%u sack=%u win=%u end=%u\n",
seq, ack, sack, win, end);
pr_debug("seq=%u ack=%u+(%d) sack=%u+(%d) win=%u end=%u\n",
seq, ack, receiver_offset, sack, receiver_offset, win, end);
pr_debug("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
"receiver end=%u maxend=%u maxwin=%u scale=%i\n",
sender->td_end, sender->td_maxend, sender->td_maxwin,
Expand Down Expand Up @@ -613,8 +634,8 @@ static bool tcp_in_window(const struct nf_conn *ct,

pr_debug("tcp_in_window: ");
nf_ct_dump_tuple(tuple);
pr_debug("seq=%u ack=%u sack =%u win=%u end=%u\n",
seq, ack, sack, win, end);
pr_debug("seq=%u ack=%u+(%d) sack=%u+(%d) win=%u end=%u\n",
seq, ack, receiver_offset, sack, receiver_offset, win, end);
pr_debug("tcp_in_window: sender end=%u maxend=%u maxwin=%u scale=%i "
"receiver end=%u maxend=%u maxwin=%u scale=%i\n",
sender->td_end, sender->td_maxend, sender->td_maxwin,
Expand Down Expand Up @@ -700,7 +721,7 @@ static bool tcp_in_window(const struct nf_conn *ct,
before(seq, sender->td_maxend + 1) ?
after(end, sender->td_end - receiver->td_maxwin - 1) ?
before(sack, receiver->td_end + 1) ?
after(ack, receiver->td_end - MAXACKWINDOW(sender)) ? "BUG"
after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1) ? "BUG"
: "ACK is under the lower bound (possible overly delayed ACK)"
: "ACK is over the upper bound (ACKed data not seen yet)"
: "SEQ is under the lower bound (already ACKed data retransmitted)"
Expand All @@ -715,39 +736,6 @@ static bool tcp_in_window(const struct nf_conn *ct,
return res;
}

#ifdef CONFIG_NF_NAT_NEEDED
/* Update sender->td_end after NAT successfully mangled the packet */
/* Caller must linearize skb at tcp header. */
void nf_conntrack_tcp_update(const struct sk_buff *skb,
unsigned int dataoff,
struct nf_conn *ct, int dir,
s16 offset)
{
const struct tcphdr *tcph = (const void *)skb->data + dataoff;
const struct ip_ct_tcp_state *sender = &ct->proto.tcp.seen[dir];
const struct ip_ct_tcp_state *receiver = &ct->proto.tcp.seen[!dir];
__u32 end;

end = segment_seq_plus_len(ntohl(tcph->seq), skb->len, dataoff, tcph);

spin_lock_bh(&ct->lock);
/*
* We have to worry for the ack in the reply packet only...
*/
if (ct->proto.tcp.seen[dir].td_end + offset == end)
ct->proto.tcp.seen[dir].td_end = end;
ct->proto.tcp.last_end = end;
spin_unlock_bh(&ct->lock);
pr_debug("tcp_update: sender end=%u maxend=%u maxwin=%u scale=%i "
"receiver end=%u maxend=%u maxwin=%u scale=%i\n",
sender->td_end, sender->td_maxend, sender->td_maxwin,
sender->td_scale,
receiver->td_end, receiver->td_maxend, receiver->td_maxwin,
receiver->td_scale);
}
EXPORT_SYMBOL_GPL(nf_conntrack_tcp_update);
#endif

#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
Expand Down

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