[ovs-dev] [PATCH v2] datapath-windows: Do not drop Ip fragments less than MIN_FRAGMENT_SIZE

[aserdean at ovn.org]

Acked-by: Alin Gabriel Serdean <aserdean at ovn.org>

Alin.

-----Mesaj original-----
De la: ovs-dev-bounces at openvswitch.org <ovs-dev-bounces at openvswitch.org> În
numele Anand Kumar
Trimis: Wednesday, March 7, 2018 1:48 AM
Către: dev at openvswitch.org
Subiect: [ovs-dev] [PATCH v2] datapath-windows: Do not drop Ip fragments
less than MIN_FRAGMENT_SIZE

Previously ipfragment module would drop any fragments less than
MIN_FRAGMENT_SIZE (400 bytes), which was added to safeguard against the
vulnerability CVE-2000-0305. This check is incorrect, since minimum size of
the Ipfragment is 68 bytes (i.e. max length of Ip Header + 8 bytes of
L4 header). So Ip fragments less than MIN_FRAGMENT_SIZE (400 bytes) is not
guranted to be malformed or illegal.

To guard against security vulnerability CVE-2000-0305, for a given ip
datagram, ipfragments should be dropped only when number of smallest
fragments recieved reaches a certain threshold.

Signed-off-by: Anand Kumar <kumaranand at vmware.com>
---
 datapath-windows/ovsext/IpFragment.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/datapath-windows/ovsext/IpFragment.c
b/datapath-windows/ovsext/IpFragment.c
index 3d5277a..d59d7cf 100644
--- a/datapath-windows/ovsext/IpFragment.c
+++ b/datapath-windows/ovsext/IpFragment.c
@@ -25,10 +25,10 @@
 #undef OVS_DBG_MOD
 #endif
 #define OVS_DBG_MOD OVS_DBG_IPFRAG
-/* Based on MIN_FRAGMENT_SIZE.*/
-#define MAX_FRAGMENTS 164
+
 #define MIN_FRAGMENT_SIZE 400
 #define MAX_IPDATAGRAM_SIZE 65535
+#define MAX_FRAGMENTS MAX_IPDATAGRAM_SIZE/MIN_FRAGMENT_SIZE + 1
 
 /* Function declarations */
 static KSTART_ROUTINE OvsIpFragmentEntryCleaner; @@ -275,10 +275,7 @@
OvsProcessIpv4Fragment(POVS_SWITCH_CONTEXT switchContext,
     offset = ntohs(ipHdr->frag_off) & IP_OFFSET;
     offset <<= 3;
     flags = ntohs(ipHdr->frag_off) & IP_MF;
-    /* Only the last fragment can be of smaller size.*/
-    if (flags && ntohs(ipHdr->tot_len) < MIN_FRAGMENT_SIZE) {
-        return NDIS_STATUS_INVALID_LENGTH;
-    }
+
     /*Copy fragment specific fields. */
     fragKey.protocol = ipHdr->protocol;
     fragKey.id = ipHdr->id;
--
2.9.3.windows.1

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