[PATCH net] sctp: fix ASCONF address change on single-homed hosts

[Andrey Misiurov <andrey.misyrov@gmail.com>]

Commit 9b2854f86f0b ("sctp: don't free the ASCONF's own transport in
DEL-IP processing") refuses a DEL-IP of the transport the ASCONF was
located by, so that a later wildcard DEL-IP cannot use it after free.

This also breaks the single-homed address change (RFC 5061 5.3.2). The
host sends [Address Parameter L] [ADD-IP S] [DEL-IP L], the association
is located by L, and DEL-IP L is now refused. The sender never gets an
all-success ASCONF-ACK, keeps src_out_of_asoc_ok set and stops sending
data, so the association stalls.

Fix the wildcard DEL-IP instead: look up the transport of the packet
source rather than reusing asconf->transport, and clear
asconf->transport when a plain DEL-IP removes it.

Fixes: 9b2854f86f0b ("sctp: don't free the ASCONF's own transport in DEL-IP processing")
Cc: stable@vger.kernel.org
Signed-off-by: Andrey Misiurov <andrey.misyrov@gmail.com>
---
 net/sctp/sm_make_chunk.c | 15 ++++++++-------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -3150,9 +3150,11 @@
 		 * packet MUST be deleted.
 		 */
 		if (af->is_any(&addr)) {
-			sctp_assoc_set_primary(asoc, asconf->transport);
-			sctp_assoc_del_nonprimary_peers(asoc,
-							asconf->transport);
+			peer = sctp_assoc_lookup_paddr(asoc, &asconf->source);
+			if (!peer)
+				return SCTP_ERROR_REQ_REFUSED;
+			sctp_assoc_set_primary(asoc, peer);
+			sctp_assoc_del_nonprimary_peers(asoc, peer);
 			return SCTP_ERROR_NO_ERROR;
 		}
 
@@ -3165,13 +3167,9 @@
 		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);
+		if (asconf->transport == peer)
+			asconf->transport = NULL;
 		break;
 	case SCTP_PARAM_SET_PRIMARY:
 		/* ADDIP Section 4.2.4