sctp: fix append error cause to ERROR chunk correctly

commit 5fa782c2
  sctp: Fix skb_over_panic resulting from multiple invalid \
    parameter errors (CVE-2010-1173) (v4)

cause 'error cause' never be add the the ERROR chunk due to
some typo when check valid length in sctp_init_cause_fixed().
Signed-off-by: NWei Yongjun <yjwei@cn.fujitsu.com>
Reviewed-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NVlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sctp/sm_make_chunk.c

@@ -141,7 +141,7 @@ int sctp_init_cause_fixed(struct sctp_chunk *chunk, __be16 cause_code,
 	len = sizeof(sctp_errhdr_t) + paylen;
 	err.length  = htons(len);
 
-	if (skb_tailroom(chunk->skb) >  len)
+	if (skb_tailroom(chunk->skb) < len)
 		return -ENOSPC;
 	chunk->subh.err_hdr = sctp_addto_chunk_fixed(chunk,
 						     sizeof(sctp_errhdr_t),
@@ -1415,7 +1415,7 @@ void *sctp_addto_chunk(struct sctp_chunk *chunk, int len, const void *data)
 void *sctp_addto_chunk_fixed(struct sctp_chunk *chunk,
 			     int len, const void *data)
 {
-	if (skb_tailroom(chunk->skb) > len)
+	if (skb_tailroom(chunk->skb) >= len)
 		return sctp_addto_chunk(chunk, len, data);
 	else
 		return NULL;