ospfd: Correct Opaque LSA Extended Link parser

Iggy Frankovic discovered another ospfd crash when performing fuzzing of OSPF
LSA packets. The crash occurs in ospf_te_parse_ext_link() function when
attemping to read Segment Routing Adjacency SID subTLVs. The original code
doesn't check if the size of the Extended Link TLVs and subTLVs have the correct
length. In presence of erronous LSA, this will cause a buffer overflow and ospfd
crashes.

This patch introduces new verification of the subTLVs size for Extended Link
TLVs and subTLVs.

Co-authored-by: Iggy Frankovic <[email protected]>
Signed-off-by: Olivier Dugeon <[email protected]>

ospfd/ospf_te.c

@@ -2620,6 +2620,7 @@ static int ospf_te_parse_ext_pref(struct ls_ted *ted, struct ospf_lsa *lsa)
 	struct ext_tlv_prefix *ext;
 	struct ext_subtlv_prefix_sid *pref_sid;
 	uint32_t label;
+	uint16_t len, size;
 
 	/* Get corresponding Subnet from Link State Data Base */
 	ext = (struct ext_tlv_prefix *)TLV_HDR_TOP(lsa->data);
@@ -2641,6 +2642,15 @@ static int ospf_te_parse_ext_pref(struct ls_ted *ted, struct ospf_lsa *lsa)
 	ote_debug("  |- Process Extended Prefix LSA %pI4 for subnet %pFX",
 		  &lsa->data->id, &pref);
 
+	/* Check TLV size with LSA size as only one TLV is allowed per LSA */
+	len = TLV_BODY_SIZE(&ext->header) - EXT_TLV_LINK_SIZE;
+	size = lsa->size - (OSPF_LSA_HEADER_SIZE + TLV_HDR_SIZE);
+	if (len != size || len <= 0) {
+		ote_debug("  |- Wrong TLV size: %u instead of %u",
+			  (uint32_t)len, (uint32_t)size);
+		return -1;
+	}
+
 	/* Initialize TLV browsing */
 	ls_pref = subnet->ls_pref;
 	pref_sid = (struct ext_subtlv_prefix_sid *)((char *)(ext) + TLV_HDR_SIZE
@@ -2751,8 +2761,17 @@ static int ospf_te_parse_ext_link(struct ls_ted *ted, struct ospf_lsa *lsa)
 	ote_debug("  |- Process Extended Link LSA %pI4 for edge %pI4",
 		  &lsa->data->id, &edge->attributes->standard.local);
 
-	/* Initialize TLV browsing */
+	/* Initialize subTLVs browsing */
 	len = TLV_BODY_SIZE(&ext->header) - EXT_TLV_LINK_SIZE;
+
+	/* Check TLV size with LSA size as only one TLV is allowed per LSA */
+	i = lsa->size - (OSPF_LSA_HEADER_SIZE + TLV_HDR_SIZE);
+	if (len != i || len <= 0) {
+		ote_debug("  |- Wrong TLV size: %u instead of %u",
+			  (uint32_t)len, (uint32_t)i);
+		return -1;
+	}
+
 	tlvh = (struct tlv_header *)((char *)(ext) + TLV_HDR_SIZE
 				     + EXT_TLV_LINK_SIZE);
 	for (; sum < len; tlvh = TLV_HDR_NEXT(tlvh)) {
@@ -2762,6 +2781,8 @@ static int ospf_te_parse_ext_link(struct ls_ted *ted, struct ospf_lsa *lsa)
 
 		switch (ntohs(tlvh->type)) {
 		case EXT_SUBTLV_ADJ_SID:
+			if (TLV_BODY_SIZE(tlvh) != EXT_SUBTLV_ADJ_SID_SIZE)
+				break;
 			adj = (struct ext_subtlv_adj_sid *)tlvh;
 			label = CHECK_FLAG(adj->flags,
 					   EXT_SUBTLV_LINK_ADJ_SID_VFLG)
@@ -2788,6 +2809,8 @@ static int ospf_te_parse_ext_link(struct ls_ted *ted, struct ospf_lsa *lsa)
 
 			break;
 		case EXT_SUBTLV_LAN_ADJ_SID:
+			if (TLV_BODY_SIZE(tlvh) != EXT_SUBTLV_LAN_ADJ_SID_SIZE)
+				break;
 			ladj = (struct ext_subtlv_lan_adj_sid *)tlvh;
 			label = CHECK_FLAG(ladj->flags,
 					   EXT_SUBTLV_LINK_ADJ_SID_VFLG)
@@ -2817,6 +2840,8 @@ static int ospf_te_parse_ext_link(struct ls_ted *ted, struct ospf_lsa *lsa)
 
 			break;
 		case EXT_SUBTLV_RMT_ITF_ADDR:
+			if (TLV_BODY_SIZE(tlvh) != EXT_SUBTLV_RMT_ITF_ADDR_SIZE)
+				break;
 			rmt = (struct ext_subtlv_rmt_itf_addr *)tlvh;
 			if (CHECK_FLAG(atr->flags, LS_ATTR_NEIGH_ADDR)
 			    && IPV4_ADDR_SAME(&atr->standard.remote,