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author | Martynas Pumputis <martynas@weave.works> | 2019-01-29 15:51:42 +0100 |
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committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2019-02-04 14:26:11 +0100 |
commit | 4e35c1cb9460240e983a01745b5f29fe3a4d8e39 (patch) | |
tree | 224dcc7e233ed0e3e70009ab1eaf432b9306f0dd | |
parent | 98bfc3414bda335dbd7fec58bde6266f991801d7 (diff) | |
download | linux-4e35c1cb9460240e983a01745b5f29fe3a4d8e39.tar.gz linux-4e35c1cb9460240e983a01745b5f29fe3a4d8e39.tar.bz2 linux-4e35c1cb9460240e983a01745b5f29fe3a4d8e39.zip |
netfilter: nf_nat: skip nat clash resolution for same-origin entries
It is possible that two concurrent packets originating from the same
socket of a connection-less protocol (e.g. UDP) can end up having
different IP_CT_DIR_REPLY tuples which results in one of the packets
being dropped.
To illustrate this, consider the following simplified scenario:
1. Packet A and B are sent at the same time from two different threads
by same UDP socket. No matching conntrack entry exists yet.
Both packets cause allocation of a new conntrack entry.
2. get_unique_tuple gets called for A. No clashing entry found.
conntrack entry for A is added to main conntrack table.
3. get_unique_tuple is called for B and will find that the reply
tuple of B is already taken by A.
It will allocate a new UDP source port for B to resolve the clash.
4. conntrack entry for B cannot be added to main conntrack table
because its ORIGINAL direction is clashing with A and the REPLY
directions of A and B are not the same anymore due to UDP source
port reallocation done in step 3.
This patch modifies nf_conntrack_tuple_taken so it doesn't consider
colliding reply tuples if the IP_CT_DIR_ORIGINAL tuples are equal.
[ Florian: simplify patch to not use .allow_clash setting
and always ignore identical flows ]
Signed-off-by: Martynas Pumputis <martynas@weave.works>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
-rw-r--r-- | net/netfilter/nf_conntrack_core.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 741b533148ba..db4d46332e86 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -1007,6 +1007,22 @@ nf_conntrack_tuple_taken(const struct nf_conntrack_tuple *tuple, } if (nf_ct_key_equal(h, tuple, zone, net)) { + /* Tuple is taken already, so caller will need to find + * a new source port to use. + * + * Only exception: + * If the *original tuples* are identical, then both + * conntracks refer to the same flow. + * This is a rare situation, it can occur e.g. when + * more than one UDP packet is sent from same socket + * in different threads. + * + * Let nf_ct_resolve_clash() deal with this later. + */ + if (nf_ct_tuple_equal(&ignored_conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple, + &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple)) + continue; + NF_CT_STAT_INC_ATOMIC(net, found); rcu_read_unlock(); return 1; |