This adds/replaces code for processing incoming ChangeL/R options.
The main difference is that:
 * mandatory FN options are now interpreted inside the function
  (there are too many individual cases to do this externally);
 * the function returns an appropriate Reset code or 0,
   which is then used to fill in the data for the Reset packet.

Old code, which is no longer used or referenced, has been removed.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
---
 net/dccp/feat.h    |    4 +-
 net/dccp/feat.c    |  180 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 net/dccp/options.c |   23 ++----
 3 files changed, 189 insertions(+), 18 deletions(-)

--- a/net/dccp/feat.h
+++ b/net/dccp/feat.h
@@ -116,8 +116,8 @@ static inline void dccp_feat_debug(const u8 type, const u8 feat, const u8 val)
 extern int  dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
 				  u8 const *list, u8 len);
 extern int  dccp_feat_register_nn(struct sock *sk, u8 feat, u64 val);
-extern int  dccp_feat_change_recv(struct sock *sk, u8 type, u8 feature,
-				  u8 *val, u8 len);
+extern int  dccp_feat_parse_options(struct sock *, struct dccp_request_sock *,
+				    u8 mand, u8 opt, u8 feat, u8 *val, u8 len);
 extern int  dccp_feat_confirm_recv(struct sock *sk, u8 type, u8 feature,
 				   u8 *val, u8 len);
 extern void dccp_feat_clean(struct dccp_minisock *dmsk);
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -237,6 +237,40 @@ static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
 	return 0;
 }
 
+/**
+ * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
+ * @fn_list: feature-negotiation list to add to
+ * @feat: one of %dccp_feature_numbers
+ * @local: whether local (1) or remote (0) @feat_num is being confirmed
+ * @fval: pointer to NN/SP value to be inserted or NULL
+ * Returns 0 on success, a Reset code for further processing otherwise.
+ */
+static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
+				  dccp_feat_val *fval)
+{
+	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
+
+	if (new == NULL)
+		return DCCP_RESET_CODE_TOO_BUSY;
+
+	new->feat_num	     = feat;
+	new->is_local	     = local;
+	new->state	     = FEAT_STABLE;	/* transition in 6.6.2 */
+	new->needs_confirm   = 1;
+	new->empty_confirm   = (fval == NULL);
+	new->val.nn	     = 0;		/* zeroes the whole structure */
+	if (!new->empty_confirm)
+		new->val     = *fval;
+	new->needs_mandatory = 0;
+
+	return 0;
+}
+
+static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
+{
+	return dccp_feat_push_confirm(fn_list, feat, local, NULL);
+}
+
 static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
 {
 	list_del(&entry->node);
@@ -955,7 +989,6 @@ static int dccp_feat_nn(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
 
 	return 0;
 }
-#endif /* (later) */
 
 static void dccp_feat_empty_confirm(struct dccp_minisock *dmsk,
 				    u8 type, u8 feature)
@@ -1066,6 +1099,7 @@ int dccp_feat_change_recv(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
 }
 
 EXPORT_SYMBOL_GPL(dccp_feat_change_recv);
+#endif	/* (later) */
 
 int dccp_feat_confirm_recv(struct sock *sk, u8 type, u8 feature,
 			   u8 *val, u8 len)
@@ -1206,6 +1240,150 @@ out_clean:
 
 EXPORT_SYMBOL_GPL(dccp_feat_clone);
 
+/**
+ * dccp_feat_change_recv  -  Process incoming ChangeL/R options
+ * @fn: feature-negotiation list to update
+ * @is_mandatory: whether the Change was preceded by a Mandatory option
+ * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
+ * @feat: one of %dccp_feature_numbers
+ * @val: NN value or SP value/preference list
+ * @len: length of @val in bytes
+ * @server: whether this node is the server (1) or the client (0)
+ */
+static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
+				u8 feat, u8 *val, u8 len, const bool server)
+{
+	u8 defval, type = dccp_feat_type(feat);
+	const bool local = (opt == DCCPO_CHANGE_R);
+	struct dccp_feat_entry *entry;
+	dccp_feat_val fval;
+
+	if (len == 0 || type == FEAT_UNKNOWN)		/* 6.1 and 6.6.8 */
+		goto unknown_feature_or_value;
+
+	/*
+	 *	Negotiation of NN features: Change R is invalid, so there is no
+	 *	simultaneous negotiation; hence we do not look up in the list.
+	 */
+	if (type == FEAT_NN) {
+		if (local || len > sizeof(fval.nn))
+			goto unknown_feature_or_value;
+
+		/* 6.3.2: "The feature remote MUST accept any valid value..." */
+		fval.nn = dccp_decode_value_var(val, len);
+		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
+			goto unknown_feature_or_value;
+
+		return dccp_feat_push_confirm(fn, feat, local, &fval);
+	}
+
+	/*
+	 *	Unidirectional/simultaneous negotiation of SP features (6.3.1)
+	 */
+	entry = dccp_feat_list_lookup(fn, feat, local);
+	if (entry == NULL) {
+		/*
+		 * No particular preferences have been registered. We deal with
+		 * this situation by assuming that all valid values are equally
+		 * acceptable, and apply the following checks:
+		 * - if the peer's list is a singleton, we accept a valid value;
+		 * - if we are the server, we first try to see if the peer (the
+		 *   client) advertises the default value. If yes, we use it,
+		 *   otherwise we accept the preferred value;
+		 * - else if we are the client, we use the first list element.
+		 */
+		if (dccp_feat_clone_sp_val(&fval, val, 1))
+			return DCCP_RESET_CODE_TOO_BUSY;
+
+		if (len > 1 && server) {
+			defval = dccp_feat_default_value(feat);
+			if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
+				fval.sp.vec[0] = defval;
+		} else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
+			kfree(fval.sp.vec);
+			goto unknown_feature_or_value;
+		}
+
+		/* Treat unsupported CCIDs like invalid values */
+		if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
+			kfree(fval.sp.vec);
+			goto not_valid_or_not_known;
+		}
+
+		return dccp_feat_push_confirm(fn, feat, local, &fval);
+
+	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
+		return 0;
+	}
+
+	if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
+		entry->empty_confirm = 0;
+	} else if (is_mandatory) {
+		return DCCP_RESET_CODE_MANDATORY_ERROR;
+	} else if (entry->state == FEAT_INITIALISING) {
+		/*
+		 * Failed simultaneous negotiation (server only): try to `save'
+		 * the connection by checking whether entry contains the default
+		 * value for @feat. If yes, send an empty Confirm to signal that
+		 * the received Change was not understood - which implies using
+		 * the default value.
+		 * If this also fails, we use Reset as the last resort.
+		 */
+		WARN_ON(!server);
+		defval = dccp_feat_default_value(feat);
+		if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
+			return DCCP_RESET_CODE_OPTION_ERROR;
+		entry->empty_confirm = 1;
+	}
+	entry->needs_confirm   = 1;
+	entry->needs_mandatory = 0;
+	entry->state	       = FEAT_STABLE;
+	return 0;
+
+unknown_feature_or_value:
+	if (!is_mandatory)
+		return dccp_push_empty_confirm(fn, feat, local);
+
+not_valid_or_not_known:
+	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
+			    : DCCP_RESET_CODE_OPTION_ERROR;
+}
+
+/**
+ * dccp_feat_parse_options  -  Process Feature-Negotiation Options
+ * @sk: for general use and used by the client during connection setup
+ * @dreq: used by the server during connection setup
+ * @mandatory: whether @opt was preceded by a Mandatory option
+ * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
+ * @feat: one of %dccp_feature_numbers
+ * @val: value contents of @opt
+ * @len: length of @val in bytes
+ * Returns 0 on success, a Reset code for ending the connection otherwise.
+ */
+int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
+			    u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
+	bool server = false;
+
+	switch (sk->sk_state) {
+	/*
+	 *	Negotiation during connection setup
+	 */
+	case DCCP_LISTEN:
+		server = true;			/* fall through */
+	case DCCP_REQUESTING:
+		switch (opt) {
+		case DCCPO_CHANGE_L:
+		case DCCPO_CHANGE_R:
+			return dccp_feat_change_recv(fn, mandatory, opt, feat,
+						     val, len, server);
+		}
+	}
+	return 0;	/* ignore FN options in all other states */
+}
+
 int dccp_feat_init(struct sock *sk)
 {
 	struct dccp_sock *dp = dccp_sk(sk);
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -135,22 +135,13 @@ int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
 				      (unsigned long long)opt_recv->dccpor_ndp);
 			break;
 		case DCCPO_CHANGE_L:
-			/* fall through */
 		case DCCPO_CHANGE_R:
 			if (pkt_type == DCCP_PKT_DATA)
 				break;
-			if (len < 2)
-				goto out_invalid_option;
-			rc = dccp_feat_change_recv(sk, opt, *value, value + 1,
-						   len - 1);
-			/*
-			 * When there is a change error, change_recv is
-			 * responsible for dealing with it.  i.e. reply with an
-			 * empty confirm.
-			 * If the change was mandatory, then we need to die.
-			 */
-			if (rc && mandatory)
-				goto out_invalid_option;
+			rc = dccp_feat_parse_options(sk, dreq, mandatory, opt,
+						    *value, value + 1, len - 1);
+			if (rc)
+				goto out_featneg_failed;
 			break;
 		case DCCPO_CONFIRM_L:
 			/* fall through */
@@ -292,8 +283,10 @@ out_nonsensical_length:
 
 out_invalid_option:
 	DCCP_INC_STATS_BH(DCCP_MIB_INVALIDOPT);
-	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_OPTION_ERROR;
-	DCCP_WARN("DCCP(%p): invalid option %d, len=%d", sk, opt, len);
+	rc = DCCP_RESET_CODE_OPTION_ERROR;
+out_featneg_failed:
+	DCCP_WARN("DCCP(%p): Option %d (len=%d) error=%u\n", sk, opt, len, rc);
+	DCCP_SKB_CB(skb)->dccpd_reset_code = rc;
 	DCCP_SKB_CB(skb)->dccpd_reset_data[0] = opt;
 	DCCP_SKB_CB(skb)->dccpd_reset_data[1] = len > 0 ? value[0] : 0;
 	DCCP_SKB_CB(skb)->dccpd_reset_data[2] = len > 1 ? value[1] : 0;
--
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