[PATCH 4/6] ip_frag: drop IPv6 fragments with unexpected headers

[Stephen Hemminger <stephen@networkplumber.org>]

DPDK version of IPv6 reassembly only handles a fragment header placed
directly after the IPv6 header. With other extension headers in the
unfragmentable part, ipv6_frag_reassemble() patches the wrong
next-header field, miscomputes the payload length, and shifts the
wrong bytes, corrupting the result.

Drop the fragment when l3_len covers more than the IPv6 and fragment
headers. RFC 8200 allows a receiver to discard packets whose extension
headers are not in the recommended order, and RFC 9099 recommends
dropping non-conforming fragmented IPv6 packets, so dropping here is
permitted rather than a deviation.

Fixes: 4f1a8f633862 ("ip_frag: add IPv6 reassembly")
Cc: stable@dpdk.org

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/ip_frag/rte_ipv6_reassembly.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/lib/ip_frag/rte_ipv6_reassembly.c b/lib/ip_frag/rte_ipv6_reassembly.c
index 0e809a01e5..7c1659002b 100644
--- a/lib/ip_frag/rte_ipv6_reassembly.c
+++ b/lib/ip_frag/rte_ipv6_reassembly.c
@@ -180,6 +180,19 @@ rte_ipv6_frag_reassemble_packet(struct rte_ip_frag_tbl *tbl,
 		return NULL;
 	}
 
+	/*
+	 * Only a fragment header directly following the IPv6 header is
+	 * supported. Other extension headers in the unfragmentable part are
+	 * not handled: ipv6_frag_reassemble() assumes l3_len covers exactly
+	 * the IPv6 and fragment headers when it patches the next-header field
+	 * and removes the fragment header. Drop the fragment rather than
+	 * produce a corrupt datagram.
+	 */
+	if (mb->l3_len != sizeof(struct rte_ipv6_hdr) + sizeof(*frag_hdr)) {
+		IP_FRAG_MBUF2DR(dr, mb);
+		return NULL;
+	}
+
 	if (unlikely(trim > 0))
 		rte_pktmbuf_trim(mb, trim);
 
-- 
2.53.0