IP reassembly must not accept data past an MF=0 fragment. Track
last fragments, reject ranges beyond them on insert, and require the
sorted rightmost fragment to be MF=0 before completing a list.
The accompanying test is added to tests/ofproto-dpif.at (using
netdev-dummy/receive with variable-built packets and precomputed IPv4
header checksums) rather than the system-traffic suite.
Assisted-by: composer-2.5-fast, Cursor
Fixes: 4ea96698f667 ("Userspace datapath: Add fragmentation handling.")
Signed-off-by: Eli Britstein <[email protected]>
---
lib/ipf.c | 36 +++++++++++++++++++--
tests/ofproto-dpif.at | 74 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 108 insertions(+), 2 deletions(-)
diff --git a/lib/ipf.c b/lib/ipf.c
index 7da8b5176..2127ce32e 100644
--- a/lib/ipf.c
+++ b/lib/ipf.c
@@ -98,6 +98,7 @@ struct ipf_frag {
struct dp_packet *pkt;
uint16_t start_data_byte;
uint16_t end_data_byte;
+ bool last_frag; /* True if this was the MF=0 fragment. */
};
/* The key for a collection of fragments potentially making up an unfragmented
@@ -397,8 +398,14 @@ ipf_list_complete(const struct ipf_list *ipf_list)
!= ipf_list->frag_list[i].start_data_byte) {
return false;
}
+
+ /* Only the final fragment may have MF=0; data past it is invalid. */
+ if (ipf_list->frag_list[i - 1].last_frag) {
+ return false;
+ }
}
- return true;
+
+ return ipf_list->frag_list[ipf_list->last_inuse_idx].last_frag;
}
/* Runs O(n) for a sorted or almost sorted list. */
@@ -859,6 +866,28 @@ ipf_is_frag_duped(const struct ipf_frag *frag_list, int
last_inuse_idx,
return false;
}
+/* Returns true if accepting this fragment would place data past an MF=0
+ * (last) fragment, which is illegal for IP reassembly. */
+static bool
+ipf_is_beyond_last_frag(const struct ipf_frag *frag_list, int last_inuse_idx,
+ uint16_t start_data_byte, uint16_t end_data_byte,
+ bool lf)
+ /* OVS_REQUIRES(ipf_lock) */
+{
+ for (int i = 0; i <= last_inuse_idx; i++) {
+ if (frag_list[i].last_frag
+ && start_data_byte > frag_list[i].end_data_byte) {
+ return true;
+ }
+
+ if (lf && frag_list[i].end_data_byte > end_data_byte) {
+ return true;
+ }
+ }
+
+ return false;
+}
+
/* Adds a fragment to a list of fragments, if the fragment is not a
* duplicate. If the fragment is a duplicate, the fragment is dropped
* to avoid the work that conntrack would do to mark the fragment
@@ -872,14 +901,17 @@ ipf_process_frag(struct ipf *ipf, struct ipf_list
*ipf_list,
{
bool duped_frag = ipf_is_frag_duped(ipf_list->frag_list,
ipf_list->last_inuse_idx, start_data_byte, end_data_byte);
+ bool beyond_last = ipf_is_beyond_last_frag(ipf_list->frag_list,
+ ipf_list->last_inuse_idx, start_data_byte, end_data_byte, lf);
int last_inuse_idx = ipf_list->last_inuse_idx;
- if (!duped_frag) {
+ if (!duped_frag && !beyond_last) {
if (last_inuse_idx < ipf_list->size - 1) {
struct ipf_frag *frag = &ipf_list->frag_list[last_inuse_idx + 1];
frag->pkt = pkt;
frag->start_data_byte = start_data_byte;
frag->end_data_byte = end_data_byte;
+ frag->last_frag = lf;
ipf_list->last_inuse_idx++;
atomic_count_inc(&ipf->nfrag);
ipf_count(ipf, v6, IPF_NFRAGS_ACCEPTED);
diff --git a/tests/ofproto-dpif.at b/tests/ofproto-dpif.at
index fbcc5a67e..3d38eddc6 100644
--- a/tests/ofproto-dpif.at
+++ b/tests/ofproto-dpif.at
@@ -5789,6 +5789,80 @@ AT_CHECK([ovs-appctl dpctl/ipf-get-status -m \
OVS_VSWITCHD_STOP
AT_CLEANUP
+AT_SETUP([ofproto-dpif - fragment handling - reject fragment beyond last])
+OVS_VSWITCHD_START
+add_of_ports br0 1 90
+
+AT_DATA([flows.txt], [dnl
+table=0 in_port=90,ip actions=ct(commit),output:1
+])
+AT_CHECK([ovs-ofctl -O OpenFlow11 replace-flows br0 flows.txt])
+
+dnl The minimum fragment size is clamped to 400 bytes, so a non-last fragment
+dnl must be at least that large to be admitted for reassembly.
+AT_CHECK([ovs-appctl dpctl/ipf-set-min-frag v4 400], [], [dnl
+setting minimum fragment size successful
+])
+
+dnl First admit a last (MF=0) fragment carrying bytes 400..799, then reject a
+dnl new fragment carrying bytes 800..1199, whose data lies entirely beyond the
+dnl end of the last fragment and so must not be reassembled.
+dnl
+dnl Packet 1 (admitted). Last fragment carrying bytes 400..799 (MF clear).
+dnl Ethernet II, Src: 50:54:00:00:00:09, Dst: 50:54:00:00:00:0a
+dnl Type: IPv4 (0x0800)
+dnl Internet Protocol Version 4, Src: 10.1.1.1, Dst: 10.1.1.2
+dnl 0100 .... = Version: 4
+dnl .... 0101 = Header Length: 20 bytes (5)
+dnl Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
+dnl Total Length: 420
+dnl Identification: 0x0020 (32)
+dnl 000. .... = Flags: 0x0 (Last fragment)
+dnl ...0 0000 0011 0010 = Fragment Offset: 400
+dnl Time to Live: 64
+dnl Protocol: UDP (17)
+dnl Header Checksum: 0x62f3
+dnl Data (400 bytes)
+eth="50 54 00 00 00 0a 50 54 00 00 00 09 08 00"
+ip1="45 00 01 a4 00 20 00 32 40 11 62 f3"
+addrs="0a 01 01 01 0a 01 01 02"
+data1=$(printf '%0*d' 800 0)
+packet1="${eth}${ip1}${addrs}${data1}"
+
+dnl Packet 2 (rejected as beyond last). Fragment carrying bytes 800..1199
+dnl (MF set), starting past packet 1's last-fragment end.
+dnl Ethernet II, Src: 50:54:00:00:00:09, Dst: 50:54:00:00:00:0a
+dnl Type: IPv4 (0x0800)
+dnl Internet Protocol Version 4, Src: 10.1.1.1, Dst: 10.1.1.2
+dnl 0100 .... = Version: 4
+dnl .... 0101 = Header Length: 20 bytes (5)
+dnl Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
+dnl Total Length: 420
+dnl Identification: 0x0020 (32)
+dnl 001. .... = Flags: 0x1 (More fragments)
+dnl ...0 0000 0110 0100 = Fragment Offset: 800
+dnl Time to Live: 64
+dnl Protocol: UDP (17)
+dnl Header Checksum: 0x42c1
+dnl Data (400 bytes)
+ip2="45 00 01 a4 00 20 20 64 40 11 42 c1"
+data2=$(printf '%0*d' 800 0)
+packet2="${eth}${ip2}${addrs}${data2}"
+
+AT_CHECK([ovs-appctl netdev-dummy/receive p90 "$packet1"])
+AT_CHECK([ovs-appctl netdev-dummy/receive p90 "$packet2"])
+
+AT_CHECK([ovs-appctl dpctl/ipf-get-status -m \
+| grep -E 'num frag:|v4 frags accepted:|v4 frags completed:|v4 frags
overlapped:'], [], [dnl
+ num frag: 1
+ v4 frags accepted: 1
+ v4 frags completed: 0
+ v4 frags overlapped: 1
+])
+
+OVS_VSWITCHD_STOP
+AT_CLEANUP
+
AT_SETUP([ofproto-dpif - handling of malformed TCP packets])
OVS_VSWITCHD_START
add_of_ports br0 1 90
--
2.43.0
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