Implement new fragment handling policy.

Until now, OVS has handled IP fragments more awkwardly than necessary.  It
has not been possible to match on L4 headers, even in fragments with offset
0 where they are actually present.  This means that there was no way to
implement ACLs that treat, say, different TCP ports differently, on
fragmented traffic; instead, all decisions for fragment forwarding had to
be made on the basis of L2 and L3 headers alone.

This commit improves the situation significantly.  It is still not possible
to match on L4 headers in fragments with nonzero offset, because that
information is simply not present in such fragments, but this commit adds
the ability to match on L4 headers for fragments with zero offset.  This
means that it becomes possible to implement ACLs that drop such "first
fragments" on the basis of L4 headers.  In practice, that effectively
blocks even fragmented traffic on an L4 basis, because the receiving IP
stack cannot reassemble a full packet when the first fragment is missing.

This commit works by adding a new "fragment type" to the kernel flow match
and making it available through OpenFlow as a new NXM field named
NXM_NX_IP_FRAG.  Because OpenFlow 1.0 explicitly says that the L4 fields
are always 0 for IP fragments, it adds a new OpenFlow fragment handling
mode that fills in the L4 fields for "first fragments".  It also enhances
ovs-ofctl to allow users to configure this new fragment handling mode and
to parse the new field.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Bug #7557.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/classifier.h b/lib/classifier.h
index db090225..d5c19f09 100644
--- a/lib/classifier.h
+++ b/lib/classifier.h
@@ -117,6 +117,8 @@ bool cls_rule_set_nw_src_masked(struct cls_rule *, ovs_be32 ip, ovs_be32 mask);
 void cls_rule_set_nw_dst(struct cls_rule *, ovs_be32);
 bool cls_rule_set_nw_dst_masked(struct cls_rule *, ovs_be32 ip, ovs_be32 mask);
 void cls_rule_set_nw_tos(struct cls_rule *, uint8_t);
+void cls_rule_set_frag(struct cls_rule *, uint8_t frag);
+void cls_rule_set_frag_masked(struct cls_rule *, uint8_t frag, uint8_t mask);
 void cls_rule_set_icmp_type(struct cls_rule *, uint8_t);
 void cls_rule_set_icmp_code(struct cls_rule *, uint8_t);
 void cls_rule_set_arp_sha(struct cls_rule *, const uint8_t[6]);