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

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

[=?gb18030?B?1uzIuMC2vvxBSUdCb3TTys/k?=]

sctp_process_asconf() caches the transport the ASCONF chunk is processed
against in asconf->transport (== chunk->transport, set once in sctp_rcv()).
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 address
(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(), keeping
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 parameter")
Cc: stable@kernel.org
Signed-off-by: Jun Yang <junvyyang@tencent.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
---
 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 sctp_association *asoc,
 		if (!peer)
 			return SCTP_ERROR_DNS_FAILED;

+		/* Don't free asconf->transport; a later wildcard DEL-IP
+		 * parameter reuses it.
+		 */
+		if (peer == asconf->transport)
+			return SCTP_ERROR_DEL_SRC_IP;
+
 		sctp_assoc_rm_peer(asoc, peer);
 		break;
 	case SCTP_PARAM_SET_PRIMARY:
--
2.55.0

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

[Jason Xing]

On Thu, Jul 16, 2026 at 11:16 AM 朱雀蓝军AIGBot邮箱 <aigbot@tencent.com> wrote:
>
> sctp_process_asconf() caches the transport the ASCONF chunk is processed
> against in asconf->transport (== chunk->transport, set once in sctp_rcv()).
> 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 address
> (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(), keeping
> 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 parameter")
> Cc: stable@kernel.org
> Signed-off-by: Jun Yang <junvyyang@tencent.com>
> Acked-by: Xin Long <lucien.xin@gmail.com>

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 sctp_association *asoc,
>                 if (!peer)
>                         return SCTP_ERROR_DNS_FAILED;
>
> +               /* Don't free asconf->transport; a later wildcard DEL-IP
> +                * parameter reuses it.
> +                */
> +               if (peer == asconf->transport)
> +                       return SCTP_ERROR_DEL_SRC_IP;
> +
>                 sctp_assoc_rm_peer(asoc, peer);
>                 break;
>         case SCTP_PARAM_SET_PRIMARY:
> --
> 2.55.0
>
>

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

[Jakub Kicinski]

On Thu, 16 Jul 2026 13:12:10 +0200 Jason Xing wrote:
> > Fixes: 42e30bf3463c ("[SCTP]: Handle the wildcard ADD-IP Address parameter")
> > Cc: stable@kernel.org
> > Signed-off-by: Jun Yang <junvyyang@tencent.com>
> > Acked-by: Xin Long <lucien.xin@gmail.com>  
> 
> It should explicitly target the net branch?

Jason, per netdev docs we discourage such trivial process complaints.