dccp: Processing Confirm options

Analogous to the previous patch, this adds code to interpret incoming Confirm
feature-negotiation options. Both functions operate on the feature-negotiation
list of either the request_sock (server) or the dccp_sock (client).

Thanks to Wei Yongjun for pointing out that it is overly restrictive to check
the entire list of confirmed SP values.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 99 insertions, 1 deletions

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 283c7fb8c7dc..bc00c038e4a5 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -104,6 +104,13 @@ static int dccp_feat_default_value(u8 feat_num)
         return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
 }
 
+/* Test for "Req'd" feature (RFC 4340, 6.4) */
+static inline int dccp_feat_must_be_understood(u8 feat_num)
+{
+        return  feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
+                feat_num == DCCPF_SEQUENCE_WINDOW;
+}
+
 /* copy constructor, fval must not already contain allocated memory */
 static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
 {
@@ -1099,7 +1106,6 @@ 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)
@@ -1154,6 +1160,7 @@ int dccp_feat_confirm_recv(struct sock *sk, u8 type, u8 feature,
 }
 
 EXPORT_SYMBOL_GPL(dccp_feat_confirm_recv);
+#endif  /* (later) */
 
 void dccp_feat_clean(struct dccp_minisock *dmsk)
 {
@@ -1350,6 +1357,93 @@ not_valid_or_not_known:
 }
 
 /**
+ * dccp_feat_confirm_recv  -  Process received Confirm options
+ * @fn: feature-negotiation list to update
+ * @is_mandatory: whether @opt was preceded by a Mandatory option
+ * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_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 server (1) or client (0)
+ */
+static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
+                                 u8 feat, u8 *val, u8 len, const bool server)
+{
+        u8 *plist, plen, type = dccp_feat_type(feat);
+        const bool local = (opt == DCCPO_CONFIRM_R);
+        struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);
+
+        if (entry == NULL) {    /* nothing queued: ignore or handle error */
+                if (is_mandatory && type == FEAT_UNKNOWN)
+                        return DCCP_RESET_CODE_MANDATORY_ERROR;
+
+                if (!local && type == FEAT_NN)          /* 6.3.2 */
+                        goto confirmation_failed;
+                return 0;
+        }
+
+        if (entry->state != FEAT_CHANGING)              /* 6.6.2 */
+                return 0;
+
+        if (len == 0) {
+                if (dccp_feat_must_be_understood(feat)) /* 6.6.7 */
+                        goto confirmation_failed;
+                /*
+                 * Empty Confirm during connection setup: this means reverting
+                 * to the `old' value, which in this case is the default. Since
+                 * we handle default values automatically when no other values
+                 * have been set, we revert to the old value by removing this
+                 * entry from the list.
+                 */
+                dccp_feat_list_pop(entry);
+                return 0;
+        }
+
+        if (type == FEAT_NN) {
+                if (len > sizeof(entry->val.nn))
+                        goto confirmation_failed;
+
+                if (entry->val.nn == dccp_decode_value_var(val, len))
+                        goto confirmation_succeeded;
+
+                DCCP_WARN("Bogus Confirm for non-existing value\n");
+                goto confirmation_failed;
+        }
+
+        /*
+         * Parsing SP Confirms: the first element of @val is the preferred
+         * SP value which the peer confirms, the remainder depends on @len.
+         * Note that only the confirmed value need to be a valid SP value.
+         */
+        if (!dccp_feat_is_valid_sp_val(feat, *val))
+                goto confirmation_failed;
+
+        if (len == 1) {         /* peer didn't supply a preference list */
+                plist = val;
+                plen  = len;
+        } else {                /* preferred value + preference list */
+                plist = val + 1;
+                plen  = len - 1;
+        }
+
+        /* Check whether the peer got the reconciliation right (6.6.8) */
+        if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
+                DCCP_WARN("Confirm selected the wrong value %u\n", *val);
+                return DCCP_RESET_CODE_OPTION_ERROR;
+        }
+        entry->val.sp.vec[0] = *val;
+
+confirmation_succeeded:
+        entry->state = FEAT_STABLE;
+        return 0;
+
+confirmation_failed:
+        DCCP_WARN("Confirmation failed\n");
+        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
@@ -1379,6 +1473,10 @@ int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
                 case DCCPO_CHANGE_R:
                         return dccp_feat_change_recv(fn, mandatory, opt, feat,
                                                      val, len, server);
+                case DCCPO_CONFIRM_R:
+                case DCCPO_CONFIRM_L:
+                        return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
+                                                      val, len, server);
                 }
         }
         return 0;       /* ignore FN options in all other states */