[PATCH net v2 2/2] sctp: discard stale INIT after handshake completion

After an association reaches ESTABLISHED, the peer’s init_tag is already
known from the handshake. Any subsequent INIT with the same init_tag is
not a valid restart, but a delayed or duplicate INIT.

Drop such INIT chunks in sctp_sf_do_unexpected_init() instead of
processing them as new association attempts.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xin Long <[email protected]>
Acked-by: Marcelo Ricardo Leitner <[email protected]>
---
v2:
  - Fix INIT tag comparison by converting the on-wire init_tag to host byte
    order before comparing it with asoc->peer.i.init_tag.
---
 net/sctp/sm_statefuns.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 7b823d759141..8e89a870780c 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -1556,6 +1556,12 @@ static enum sctp_disposition sctp_sf_do_unexpected_init(
 	/* Tag the variable length parameters.  */
 	chunk->param_hdr.v = skb_pull(chunk->skb, sizeof(struct sctp_inithdr));
 
+	if (asoc->state >= SCTP_STATE_ESTABLISHED) {
+		/* Discard INIT matching peer vtag after handshake completion (stale INIT). */
+		if (ntohl(chunk->subh.init_hdr->init_tag) == asoc->peer.i.init_tag)
+			return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
+	}
+
 	/* Verify the INIT chunk before processing it. */
 	err_chunk = NULL;
 	if (!sctp_verify_init(net, ep, asoc, chunk->chunk_hdr->type,
-- 
2.47.1