[PATCH] sctp: reject forged cookie peer_addr with unknown address family

[Xingyuan Mo <hdthky0@gmail.com>]

When cookie authentication is disabled, COOKIE-ECHO peer_addr is
attacker-controlled. An invalid sa_family made sctp_get_af_specific()
return NULL and crash in sctp_transport_init() on
af_specific->sockaddr_len. Reject non-INET/INET6 families in
sctp_unpack_cookie(), and also bail in sctp_transport_new() if
af_specific is missing.

  BUG: KASAN: null-ptr-deref in sctp_transport_new+0xa7/0x350
  Read of size 4 at addr 00000000000000b4 by task poc/682
  Call Trace:
   <IRQ>
   sctp_transport_new+0xa7/0x350
   sctp_assoc_add_peer+0x153/0x850
   sctp_process_init+0xf9/0x1180
   sctp_sf_do_5_1D_ce+0x464/0xbc0
   sctp_do_sm+0x114/0x2990
   sctp_endpoint_bh_rcv+0x280/0x430
   sctp_inq_push+0xdd/0x100
   sctp_rcv+0x17f5/0x1ae0
   sctp4_rcv+0x2b/0x40
   ip_protocol_deliver_rcu+0x25b/0x270
   ip_local_deliver+0xd1/0xe0
   </IRQ>
  Kernel panic - not syncing: Fatal exception in interrupt

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: opencode:deepseek-v4
Signed-off-by: Xingyuan Mo <hdthky0@gmail.com>
---
 net/sctp/sm_make_chunk.c | 4 ++++
 net/sctp/transport.c     | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 84a4c97d0f75..7c8fe4b38cd1 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1855,6 +1855,10 @@ struct sctp_association *sctp_unpack_cookie(
 	if (!sctp_auth_verify_cookie_params(ep, bear_cookie))
 		goto malformed;
 
+	if (bear_cookie->peer_addr.sa.sa_family != AF_INET &&
+	    bear_cookie->peer_addr.sa.sa_family != AF_INET6)
+		goto malformed;
+
 	/* Populate the association from the cookie.  */
 	memcpy(&retval->c, bear_cookie, sizeof(*bear_cookie));
 
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index 6ea55b9fbde4..cd1a604d6f8e 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -92,6 +92,9 @@ struct sctp_transport *sctp_transport_new(struct net *net,
 {
 	struct sctp_transport *transport;
 
+	if (!sctp_get_af_specific(addr->sa.sa_family))
+		return NULL;
+
 	transport = kzalloc_obj(*transport, gfp);
 	if (!transport)
 		return NULL;
-- 
2.43.0