3 files changed, 47 insertions, 4 deletions

diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index 1881527bdcd7..e656dafb5d96 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -443,6 +443,7 @@ static inline int dccp_ack_pending(const struct sock *sk)
 }
 
 extern int  dccp_feat_finalise_settings(struct dccp_sock *dp);
+extern int  dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq);
 extern void dccp_feat_list_purge(struct list_head *fn_list);
 
 extern int dccp_insert_options(struct sock *sk, struct sk_buff *skb);
diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 4c4144147325..4f86a48723f6 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -166,6 +166,18 @@ static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
  * - SP values are always freshly allocated
  * - list is sorted in increasing order of feature number (faster lookup)
  */
+static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
+                                                     u8 feat_num, bool is_local)
+{
+        struct dccp_feat_entry *entry;
+
+        list_for_each_entry(entry, fn_list, node)
+                if (entry->feat_num == feat_num && entry->is_local == is_local)
+                        return entry;
+                else if (entry->feat_num > feat_num)
+                        break;
+        return NULL;
+}
 
 /**
  * dccp_feat_entry_new  -  Central list update routine (called by all others)
@@ -560,6 +572,31 @@ int dccp_feat_finalise_settings(struct dccp_sock *dp)
         return 0;
 }
 
+/**
+ * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
+ * It is the server which resolves the dependencies once the CCID has been
+ * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
+ */
+int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
+{
+        struct list_head *fn = &dreq->dreq_featneg;
+        struct dccp_feat_entry *entry;
+        u8 is_local, ccid;
+
+        for (is_local = 0; is_local <= 1; is_local++) {
+                entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);
+
+                if (entry != NULL && !entry->empty_confirm)
+                        ccid = entry->val.sp.vec[0];
+                else
+                        ccid = dccp_feat_default_value(DCCPF_CCID);
+
+                if (dccp_feat_propagate_ccid(fn, ccid, is_local))
+                        return -1;
+        }
+        return 0;
+}
+
 static int dccp_feat_update_ccid(struct sock *sk, u8 type, u8 new_ccid_nr)
 {
         struct dccp_sock *dp = dccp_sk(sk);
diff --git a/net/dccp/output.c b/net/dccp/output.c
index 92f3f6f2ef51..fea30cdc0bee 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -339,10 +339,12 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
         DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
         DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_iss;
 
-        if (dccp_insert_options_rsk(dreq, skb)) {
-                kfree_skb(skb);
-                return NULL;
-        }
+        /* Resolve feature dependencies resulting from choice of CCID */
+        if (dccp_feat_server_ccid_dependencies(dreq))
+                goto response_failed;
+
+        if (dccp_insert_options_rsk(dreq, skb))
+                goto response_failed;
 
         /* Build and checksum header */
         dh = dccp_zeroed_hdr(skb, dccp_header_size);
@@ -363,6 +365,9 @@ struct sk_buff *dccp_make_response(struct sock *sk, struct dst_entry *dst,
         inet_rsk(req)->acked = 1;
         DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
         return skb;
+response_failed:
+        kfree_skb(skb);
+        return NULL;
 }
 
 EXPORT_SYMBOL_GPL(dccp_make_response);