sctp: Follow security requirement of responding with 1 packet

RFC 4960, Section 11.4. Protection of Non-SCTP-Capable Hosts

When an SCTP stack receives a packet containing multiple control or
DATA chunks and the processing of the packet requires the sending of
multiple chunks in response, the sender of the response chunk(s) MUST
NOT send more than one packet.  If bundling is supported, multiple
response chunks that fit into a single packet MAY be bundled together
into one single response packet.  If bundling is not supported, then
the sender MUST NOT send more than one response chunk and MUST
discard all other responses.  Note that this rule does NOT apply to a
SACK chunk, since a SACK chunk is, in itself, a response to DATA and
a SACK does not require a response of more DATA.

We implement this by not servicing our outqueue until we reach the end
of the packet.  This enables maximum bundling.  We also identify
'response' chunks and make sure that we only send 1 packet when sending
such chunks.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 11 deletions

diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
index 0c9d5a6950fe..b66a41d03c0d 100644
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -795,8 +795,6 @@ sctp_disposition_t sctp_sf_do_5_1D_ce(const struct sctp_endpoint *ep,
                 sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_START,
                                 SCTP_TO(SCTP_EVENT_TIMEOUT_AUTOCLOSE));
 
-        sctp_add_cmd_sf(commands, SCTP_CMD_TRANSMIT, SCTP_NULL());
-
         /* This will send the COOKIE ACK */
         sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));
 
@@ -883,7 +881,6 @@ sctp_disposition_t sctp_sf_do_5_1E_ca(const struct sctp_endpoint *ep,
         if (asoc->autoclose)
                 sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_START,
                                 SCTP_TO(SCTP_EVENT_TIMEOUT_AUTOCLOSE));
-        sctp_add_cmd_sf(commands, SCTP_CMD_TRANSMIT, SCTP_NULL());
 
         /* It may also notify its ULP about the successful
          * establishment of the association with a Communication Up
@@ -1781,7 +1778,6 @@ static sctp_disposition_t sctp_sf_do_dupcook_b(const struct sctp_endpoint *ep,
                 goto nomem;
 
         sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));
-        sctp_add_cmd_sf(commands, SCTP_CMD_TRANSMIT, SCTP_NULL());
 
         /* RFC 2960 5.1 Normal Establishment of an Association
          *
@@ -1898,12 +1894,13 @@ static sctp_disposition_t sctp_sf_do_dupcook_d(const struct sctp_endpoint *ep,
 
                 }
         }
-        sctp_add_cmd_sf(commands, SCTP_CMD_TRANSMIT, SCTP_NULL());
 
         repl = sctp_make_cookie_ack(new_asoc, chunk);
         if (!repl)
                 goto nomem;
 
+        sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));
+
         if (ev)
                 sctp_add_cmd_sf(commands, SCTP_CMD_EVENT_ULP,
                                 SCTP_ULPEVENT(ev));
@@ -1911,9 +1908,6 @@ static sctp_disposition_t sctp_sf_do_dupcook_d(const struct sctp_endpoint *ep,
                 sctp_add_cmd_sf(commands, SCTP_CMD_EVENT_ULP,
                                         SCTP_ULPEVENT(ai_ev));
 
-        sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(repl));
-        sctp_add_cmd_sf(commands, SCTP_CMD_TRANSMIT, SCTP_NULL());
-
         return SCTP_DISPOSITION_CONSUME;
 
 nomem:
@@ -3970,9 +3964,6 @@ sctp_disposition_t sctp_sf_unk_chunk(const struct sctp_endpoint *ep,
                 return sctp_sf_pdiscard(ep, asoc, type, arg, commands);
                 break;
         case SCTP_CID_ACTION_DISCARD_ERR:
-                /* Discard the packet.  */
-                sctp_sf_pdiscard(ep, asoc, type, arg, commands);
-
                 /* Generate an ERROR chunk as response. */
                 hdr = unk_chunk->chunk_hdr;
                 err_chunk = sctp_make_op_error(asoc, unk_chunk,
@@ -3982,6 +3973,9 @@ sctp_disposition_t sctp_sf_unk_chunk(const struct sctp_endpoint *ep,
                         sctp_add_cmd_sf(commands, SCTP_CMD_REPLY,
                                         SCTP_CHUNK(err_chunk));
                 }
+
+                /* Discard the packet.  */
+                sctp_sf_pdiscard(ep, asoc, type, arg, commands);
                 return SCTP_DISPOSITION_CONSUME;
                 break;
         case SCTP_CID_ACTION_SKIP: