[Devel] [PATCH VZ10] sctp: don't free the ASCONF's own transport in DEL-IP processing

[Pavel Tikhomirov <ptikhomirov@virtuozzo.com>]

From: Jun Yang <junvyyang@tencent.com>

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>
Link: https://patch.msgid.link/tencent_73762ED1DF08CC9D5F5F61954B01350CFE0A@qq.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

CVE-2026-64564
https://virtuozzo.atlassian.net/browse/VSTOR-140910
(cherry picked from commit 9b2854f86f0b56e9027d68e7a3fc909d1a9b566f)
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.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 07e220b8a4af5..b3fb015409031 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -3156,6 +3156,12 @@ 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_REQ_REFUSED;
+
 		sctp_assoc_rm_peer(asoc, peer);
 		break;
 	case SCTP_PARAM_SET_PRIMARY:
-- 
2.55.0