sctp: process duplicated strreset out and addstrm out requests correctly

Now sctp stream reconf will process a request again even if it's seqno is
less than asoc->strreset_inseq.

If one request has been done successfully and some data chunks have been
accepted and then a duplicated strreset out request comes, the streamin's
ssn will be cleared. It will cause that stream will never receive chunks
any more because of unsynchronized ssn. It allows a replay attack.

A similar issue also exists when processing addstrm out requests. It will
cause more extra streams being added.

This patch is to fix it by saving the last 2 results into asoc. When a
duplicated strreset out or addstrm out request is received, reply it with
bad seqno if it's seqno < asoc->strreset_inseq - 2, and reply it with the
result saved in asoc if it's seqno >= asoc->strreset_inseq - 2.

Note that it saves last 2 results instead of only last 1 result, because
two requests can be sent together in one chunk.

And note that when receiving a duplicated request, the receiver side will
still reply it even if the peer has received the response. It's safe, As
the response will be dropped by the peer.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index b751399aa6b7..a8b38e123f97 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1889,6 +1889,7 @@ struct sctp_association {
 
 	__u32 strreset_outseq; /* Update after receiving response */
 	__u32 strreset_inseq; /* Update after receiving request */
+	__u32 strreset_result[2]; /* save the results of last 2 responses */
 
 	struct sctp_chunk *strreset_chunk; /* save request chunk */