Date:   Fri, 4 May 2018 19:33:37 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net, Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: delay the authentication for the duplicated
 cookie-echo chunk

On Fri, May 04, 2018 at 05:05:10PM +0800, Xin Long wrote:
> Now sctp only delays the authentication for the normal cookie-echo
> chunk by setting chunk->auth_chunk in sctp_endpoint_bh_rcv(). But
> for the duplicated one with auth, in sctp_assoc_bh_rcv(), it does
> authentication first based on the old asoc, which will definitely
> fail due to the different auth info in the old asoc.
>
> The duplicated cookie-echo chunk will create a new asoc with the
> auth info from this chunk, and the authentication should also be
> done with the new asoc's auth info for all of the collision 'A',
> 'B' and 'D'. Otherwise, the duplicated cookie-echo chunk with auth
> will never pass the authentication and create the new connection.
>
> This issue exists since very beginning, and this fix is to make
> sctp_assoc_bh_rcv() follow the way sctp_assoc_bh_rcv() does for
   I guess you meant sctp_endpoint_bh_rcv here --^ right?

Other than this LGTM

> the normal cookie-echo chunk to delay the authentication.
>
> While at it, remove the unused params from sctp_sf_authenticate()
> and define sctp_auth_chunk_verify() used for all the places that
> do the delayed authentication.
>
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/sctp/associola.c    | 30 ++++++++++++++++-
>  net/sctp/sm_statefuns.c | 86 ++++++++++++++++++++++++++-----------------------
>  2 files changed, 75 insertions(+), 41 deletions(-)
>
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 837806d..a47179d 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1024,8 +1024,9 @@ static void sctp_assoc_bh_rcv(struct work_struct *work)
>  	struct sctp_endpoint *ep;
>  	struct sctp_chunk *chunk;
>  	struct sctp_inq *inqueue;
> -	int state;
> +	int first_time = 1;	/* is this the first time through the loop */
>  	int error = 0;
> +	int state;
>
>  	/* The association should be held so we should be safe. */
>  	ep = asoc->ep;
> @@ -1036,6 +1037,30 @@ static void sctp_assoc_bh_rcv(struct work_struct *work)
>  		state = asoc->state;
>  		subtype = SCTP_ST_CHUNK(chunk->chunk_hdr->type);
>
> +		/* If the first chunk in the packet is AUTH, do special
> +		 * processing specified in Section 6.3 of SCTP-AUTH spec
> +		 */
> +		if (first_time && subtype.chunk == SCTP_CID_AUTH) {
> +			struct sctp_chunkhdr *next_hdr;
> +
> +			next_hdr = sctp_inq_peek(inqueue);
> +			if (!next_hdr)
> +				goto normal;
> +
> +			/* If the next chunk is COOKIE-ECHO, skip the AUTH
> +			 * chunk while saving a pointer to it so we can do
> +			 * Authentication later (during cookie-echo
> +			 * processing).
> +			 */
> +			if (next_hdr->type == SCTP_CID_COOKIE_ECHO) {
> +				chunk->auth_chunk = skb_clone(chunk->skb,
> +							      GFP_ATOMIC);
> +				chunk->auth = 1;
> +				continue;
> +			}
> +		}
> +
> +normal:
>  		/* SCTP-AUTH, Section 6.3:
>  		 *    The receiver has a list of chunk types which it expects
>  		 *    to be received only after an AUTH-chunk.  This list has
> @@ -1074,6 +1099,9 @@ static void sctp_assoc_bh_rcv(struct work_struct *work)
>  		/* If there is an error on chunk, discard this packet. */
>  		if (error && chunk)
>  			chunk->pdiscard = 1;
> +
> +		if (first_time)
> +			first_time = 0;
>  	}
>  	sctp_association_put(asoc);
>  }
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 28c070e..c9ae340 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -153,10 +153,7 @@ static enum sctp_disposition sctp_sf_violation_chunk(
>  					struct sctp_cmd_seq *commands);
>
>  static enum sctp_ierror sctp_sf_authenticate(
> -					struct net *net,
> -					const struct sctp_endpoint *ep,
>  					const struct sctp_association *asoc,
> -					const union sctp_subtype type,
>  					struct sctp_chunk *chunk);
>
>  static enum sctp_disposition __sctp_sf_do_9_1_abort(
> @@ -626,6 +623,38 @@ enum sctp_disposition sctp_sf_do_5_1C_ack(struct net *net,
>  	return SCTP_DISPOSITION_CONSUME;
>  }
>
> +static bool sctp_auth_chunk_verify(struct net *net, struct sctp_chunk *chunk,
> +				   const struct sctp_association *asoc)
> +{
> +	struct sctp_chunk auth;
> +
> +	if (!chunk->auth_chunk)
> +		return true;
> +
> +	/* SCTP-AUTH:  auth_chunk pointer is only set when the cookie-echo
> +	 * is supposed to be authenticated and we have to do delayed
> +	 * authentication.  We've just recreated the association using
> +	 * the information in the cookie and now it's much easier to
> +	 * do the authentication.
> +	 */
> +
> +	/* Make sure that we and the peer are AUTH capable */
> +	if (!net->sctp.auth_enable || !asoc->peer.auth_capable)
> +		return false;
> +
> +	/* set-up our fake chunk so that we can process it */
> +	auth.skb = chunk->auth_chunk;
> +	auth.asoc = chunk->asoc;
> +	auth.sctp_hdr = chunk->sctp_hdr;
> +	auth.chunk_hdr = (struct sctp_chunkhdr *)
> +				skb_push(chunk->auth_chunk,
> +					 sizeof(struct sctp_chunkhdr));
> +	skb_pull(chunk->auth_chunk, sizeof(struct sctp_chunkhdr));
> +	auth.transport = chunk->transport;
> +
> +	return sctp_sf_authenticate(asoc, &auth) == SCTP_IERROR_NO_ERROR;
> +}
> +
>  /*
>   * Respond to a normal COOKIE ECHO chunk.
>   * We are the side that is being asked for an association.
> @@ -763,37 +792,9 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net,
>  	if (error)
>  		goto nomem_init;
>
> -	/* SCTP-AUTH:  auth_chunk pointer is only set when the cookie-echo
> -	 * is supposed to be authenticated and we have to do delayed
> -	 * authentication.  We've just recreated the association using
> -	 * the information in the cookie and now it's much easier to
> -	 * do the authentication.
> -	 */
> -	if (chunk->auth_chunk) {
> -		struct sctp_chunk auth;
> -		enum sctp_ierror ret;
> -
> -		/* Make sure that we and the peer are AUTH capable */
> -		if (!net->sctp.auth_enable || !new_asoc->peer.auth_capable) {
> -			sctp_association_free(new_asoc);
> -			return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
> -		}
> -
> -		/* set-up our fake chunk so that we can process it */
> -		auth.skb = chunk->auth_chunk;
> -		auth.asoc = chunk->asoc;
> -		auth.sctp_hdr = chunk->sctp_hdr;
> -		auth.chunk_hdr = (struct sctp_chunkhdr *)
> -					skb_push(chunk->auth_chunk,
> -						 sizeof(struct sctp_chunkhdr));
> -		skb_pull(chunk->auth_chunk, sizeof(struct sctp_chunkhdr));
> -		auth.transport = chunk->transport;
> -
> -		ret = sctp_sf_authenticate(net, ep, new_asoc, type, &auth);
> -		if (ret != SCTP_IERROR_NO_ERROR) {
> -			sctp_association_free(new_asoc);
> -			return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
> -		}
> +	if (!sctp_auth_chunk_verify(net, chunk, new_asoc)) {
> +		sctp_association_free(new_asoc);
> +		return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands);
>  	}
>
>  	repl = sctp_make_cookie_ack(new_asoc, chunk);
> @@ -1797,13 +1798,15 @@ static enum sctp_disposition sctp_sf_do_dupcook_a(
>  	if (sctp_auth_asoc_init_active_key(new_asoc, GFP_ATOMIC))
>  		goto nomem;
>
> +	if (!sctp_auth_chunk_verify(net, chunk, new_asoc))
> +		return SCTP_DISPOSITION_DISCARD;
> +
>  	/* Make sure no new addresses are being added during the
>  	 * restart.  Though this is a pretty complicated attack
>  	 * since you'd have to get inside the cookie.
>  	 */
> -	if (!sctp_sf_check_restart_addrs(new_asoc, asoc, chunk, commands)) {
> +	if (!sctp_sf_check_restart_addrs(new_asoc, asoc, chunk, commands))
>  		return SCTP_DISPOSITION_CONSUME;
> -	}
>
>  	/* If the endpoint is in the SHUTDOWN-ACK-SENT state and recognizes
>  	 * the peer has restarted (Action A), it MUST NOT setup a new
> @@ -1912,6 +1915,9 @@ static enum sctp_disposition sctp_sf_do_dupcook_b(
>  	if (sctp_auth_asoc_init_active_key(new_asoc, GFP_ATOMIC))
>  		goto nomem;
>
> +	if (!sctp_auth_chunk_verify(net, chunk, new_asoc))
> +		return SCTP_DISPOSITION_DISCARD;
> +
>  	/* Update the content of current association.  */
>  	sctp_add_cmd_sf(commands, SCTP_CMD_UPDATE_ASSOC, SCTP_ASOC(new_asoc));
>  	sctp_add_cmd_sf(commands, SCTP_CMD_NEW_STATE,
> @@ -2009,6 +2015,9 @@ static enum sctp_disposition sctp_sf_do_dupcook_d(
>  	 * a COOKIE ACK.
>  	 */
>
> +	if (!sctp_auth_chunk_verify(net, chunk, asoc))
> +		return SCTP_DISPOSITION_DISCARD;
> +
>  	/* Don't accidentally move back into established state. */
>  	if (asoc->state < SCTP_STATE_ESTABLISHED) {
>  		sctp_add_cmd_sf(commands, SCTP_CMD_TIMER_STOP,
> @@ -4171,10 +4180,7 @@ enum sctp_disposition sctp_sf_eat_fwd_tsn_fast(
>   * The return value is the disposition of the chunk.
>   */
>  static enum sctp_ierror sctp_sf_authenticate(
> -					struct net *net,
> -					const struct sctp_endpoint *ep,
>  					const struct sctp_association *asoc,
> -					const union sctp_subtype type,
>  					struct sctp_chunk *chunk)
>  {
>  	struct sctp_shared_key *sh_key = NULL;
> @@ -4275,7 +4281,7 @@ enum sctp_disposition sctp_sf_eat_auth(struct net *net,
>  						  commands);
>
>  	auth_hdr = (struct sctp_authhdr *)chunk->skb->data;
> -	error = sctp_sf_authenticate(net, ep, asoc, type, chunk);
> +	error = sctp_sf_authenticate(asoc, chunk);
>  	switch (error) {
>  	case SCTP_IERROR_AUTH_BAD_HMAC:
>  		/* Generate the ERROR chunk and discard the rest
> --
> 2.1.0
>
> --
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