__sctp_rcv_asconf_lookup() in net/sctp/input.c only checks that the ASCONF chunk can hold the ADDIP header and a parameter header, then calls af->from_addr_param(), which reads the full address (16 bytes for IPv6) trusting the parameter's declared length. An unauthenticated peer can send a truncated trailing ASCONF chunk that declares an IPv6 address parameter but stops after the 4-byte parameter header; reached from the no-association lookup path, from_addr_param() then reads uninitialized bytes past the parameter. Impact: an unauthenticated SCTP peer makes the receive path read up to 16 bytes of uninitialized memory past a truncated ASCONF address parameter. The sibling __sctp_rcv_init_lookup() bounds parameters with sctp_walk_params(); this path open-codes the fetch and omits the bound. Verify the whole address parameter lies within the chunk before from_addr_param() reads it, the same class of fix as commit 51e5ad549c43 ("net: sctp: fix KMSAN uninit-value in sctp_inq_pop"). Fixes: df2185771439 ("[SCTP]: Update association lookup to look at ASCONF chunks as well") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito --- net/sctp/input.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/net/sctp/input.c b/net/sctp/input.c --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -1196,6 +1196,7 @@ static struct sctp_association *__sctp_rcv_asconf_lookup( struct sctp_addip_chunk *asconf = (struct sctp_addip_chunk *)ch; struct sctp_af *af; union sctp_addr_param *param; union sctp_addr paddr; + __u16 plen; if (ntohs(ch->length) < sizeof(*asconf) + sizeof(struct sctp_paramhdr)) return NULL; @@ -1204,6 +1205,16 @@ static struct sctp_association *__sctp_rcv_asconf_lookup( /* Skip over the ADDIP header and find the Address parameter */ param = (union sctp_addr_param *)(asconf + 1); + /* The whole address parameter must lie within the chunk before + * af->from_addr_param() reads the variable-length address; otherwise a + * truncated trailing ASCONF chunk lets it read uninitialized bytes past + * the parameter. Mirror the bound sctp_walk_params() applies on the + * INIT path. + */ + plen = ntohs(param->p.length); + if (plen < sizeof(struct sctp_paramhdr) || + (u8 *)param + plen > (u8 *)ch + ntohs(ch->length)) + return NULL; + af = sctp_get_af_specific(param_type2af(param->p.type)); if (unlikely(!af)) return NULL;