sctp: add vtag check in sctp_sf_ootb

sctp_sf_ootb() is called when processing DATA chunk in closed state,
and many other places are also using it.

The vtag in the chunk's sctphdr should be verified, otherwise, as
later in chunk length check, it may send abort with the existent
asoc's vtag, which can be exploited by one to cook a malicious
chunk to terminate a SCTP asoc.

When fails to verify the vtag from the chunk, this patch sets asoc
to NULL, so that the abort will be made with the vtag from the
received chunk later.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: NXin Long <lucien.xin@gmail.com>
Acked-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>

net/sctp/sm_statefuns.c

@@ -3688,6 +3688,9 @@ enum sctp_disposition sctp_sf_ootb(struct net *net,
 
 	SCTP_INC_STATS(net, SCTP_MIB_OUTOFBLUES);
 
+	if (asoc && !sctp_vtag_verify(chunk, asoc))
+		asoc = NULL;
+
 	ch = (struct sctp_chunkhdr *)chunk->chunk_hdr;
 	do {
 		/* Report violation if the chunk is less then minimal */