Re: [PATCH] sctp: don't free the ASCONF's own transport in DEL-IP processing

On Thu, Jul 16, 2026 at 11:16=E2=80=AFAM =E6=9C=B1=E9=9B=80=E8=93=9D=E5=86=
=9BAIGBot=E9=82=AE=E7=AE=B1 <[email protected]> wrote:
>
> sctp_process_asconf() caches the transport the ASCONF chunk is processed
> against in asconf->transport (=3D=3D chunk->transport, set once in sctp_r=
cv()).
> For an ASCONF located through its Address Parameter by
> __sctp_rcv_asconf_lookup(), that cached transport corresponds to the
> Address Parameter, which need not be the packet's source address.
>
> sctp_process_asconf_param() rejects a DEL-IP for the packet source addres=
s
> (ADDIP D8, SCTP_ERROR_DEL_SRC_IP), but nothing protects asconf->transport=
.
> A single ASCONF can therefore carry, in order:
>
>     [Address Parameter L] [DEL-IP L] [DEL-IP 0.0.0.0]
>
> where L differs from the source. The DEL-IP for L passes the D8 check and
> calls sctp_assoc_rm_peer() on the transport that asconf->transport still
> points at, freeing it (RCU-deferred). The following wildcard DEL-IP then
> reuses the now-dangling asconf->transport in sctp_assoc_set_primary() and
> sctp_assoc_del_nonprimary_peers(): set_primary() dereferences the freed
> transport (->ipaddr, ->state) and plants the dangling pointer into
> asoc->peer.primary_path / active_path, and del_nonprimary_peers(), keepin=
g
> only the pointer that is no longer on the list, removes every real
> transport, leaving the association with a transport_count of 0 and
> primary_path/active_path pointing at freed memory.
>
> Reject a DEL-IP that targets the transport the ASCONF is being processed
> against, mirroring the existing source-address guard, so the wildcard
> branch can never reuse a freed transport.
>
> Fixes: 42e30bf3463c ("[SCTP]: Handle the wildcard ADD-IP Address paramete=
r")
> Cc: [email protected]
> Signed-off-by: Jun Yang <[email protected]>
> Acked-by: Xin Long <[email protected]>

It should explicitly target the net branch?

Thanks,
Jason

> ---
>  net/sctp/sm_make_chunk.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 8adac9e0cd66..b14251214896 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -3153,6 +3153,12 @@ static __be16 sctp_process_asconf_param(struct sct=
p_association *asoc,
>                 if (!peer)
>                         return SCTP_ERROR_DNS_FAILED;
>
> +               /* Don't free asconf->transport; a later wildcard DEL-IP
> +                * parameter reuses it.
> +                */
> +               if (peer =3D=3D asconf->transport)
> +                       return SCTP_ERROR_DEL_SRC_IP;
> +
>                 sctp_assoc_rm_peer(asoc, peer);
>                 break;
>         case SCTP_PARAM_SET_PRIMARY:
> --
> 2.55.0
>
>