2 files changed, 17 insertions, 0 deletions

diff --git a/net/dccp/feat.h b/net/dccp/feat.h
index 90d16caf5457..602e0a7294ba 100644
--- a/net/dccp/feat.h
+++ b/net/dccp/feat.h
@@ -138,4 +138,6 @@ extern int  dccp_feat_init(struct sock *sk);
 
 extern void dccp_encode_value_var(const u64 value, u8 *to, const u8 len);
 extern u64  dccp_decode_value_var(const u8 *bf, const u8 len);
+
+extern int  dccp_insert_option_mandatory(struct sk_buff *skb);
 #endif /* _DCCP_FEAT_H */
diff --git a/net/dccp/options.c b/net/dccp/options.c
index 9cb0ff894052..676d53065de9 100644
--- a/net/dccp/options.c
+++ b/net/dccp/options.c
@@ -467,6 +467,21 @@ static int dccp_insert_option_timestamp_echo(struct dccp_sock *dp,
         return 0;
 }
 
+/**
+ * dccp_insert_option_mandatory  -  Mandatory option (5.8.2)
+ * Note that since we are using skb_push, this function needs to be called
+ * _after_ inserting the option it is supposed to influence (stack order).
+ */
+int dccp_insert_option_mandatory(struct sk_buff *skb)
+{
+        if (DCCP_SKB_CB(skb)->dccpd_opt_len >= DCCP_MAX_OPT_LEN)
+                return -1;
+
+        DCCP_SKB_CB(skb)->dccpd_opt_len++;
+        *skb_push(skb, 1) = DCCPO_MANDATORY;
+        return 0;
+}
+
 static int dccp_insert_feat_opt(struct sk_buff *skb, u8 type, u8 feat,
                                 u8 *val, u8 len)
 {