From a3a76f1ea3318060195aff762468d0af98a36608 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Duda?= <lukasz.duda@nordicsemi.no>
Date: Mon, 21 Dec 2020 16:29:11 +0100
Subject: [PATCH] [dns-client] randomize ID of outgoing query (#5981)

---
 src/core/net/dns_client.cpp | 27 +++++++++++++++++++++------
 src/core/net/dns_client.hpp |  5 +++--
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/core/net/dns_client.cpp b/src/core/net/dns_client.cpp
index e922b3236..c59fc9b01 100644
--- a/src/core/net/dns_client.cpp
+++ b/src/core/net/dns_client.cpp
@@ -50,7 +50,6 @@ namespace Dns {
 
 Client::Client(Instance &aInstance)
     : mSocket(aInstance)
-    , mMessageId(0)
     , mRetransmissionTimer(aInstance, Client::HandleRetransmissionTimer, this)
 {
 }
@@ -89,10 +88,13 @@ otError Client::Query(const QueryInfo &aQuery, ResponseHandler aHandler, void *a
     Message *     messageCopy = nullptr;
     Header        header;
     QuestionAaaa  question;
+    uint16_t      messageId;
 
     VerifyOrExit(aQuery.IsValid(), error = OT_ERROR_INVALID_ARGS);
 
-    header.SetMessageId(mMessageId++);
+    SuccessOrExit(error = GenerateUniqueRandomId(messageId));
+
+    header.SetMessageId(messageId);
     header.SetType(Header::kTypeQuery);
     header.SetQueryType(Header::kQueryTypeStandard);
 
@@ -199,6 +201,19 @@ exit:
     }
 }
 
+otError Client::GenerateUniqueRandomId(uint16_t &aRandomId)
+{
+    otError error;
+
+    do
+    {
+        SuccessOrExit(error = Random::Crypto::FillBuffer(reinterpret_cast<uint8_t *>(&aRandomId), sizeof(aRandomId)));
+    } while (FindQueryById(aRandomId) != nullptr);
+
+exit:
+    return error;
+}
+
 otError Client::CompareQuestions(Message &aMessageResponse, Message &aMessageQuery, uint16_t &aOffset)
 {
     otError  error = OT_ERROR_NONE;
@@ -228,7 +243,7 @@ exit:
     return error;
 }
 
-Message *Client::FindRelatedQuery(const Header &aResponseHeader, QueryMetadata &aQueryMetadata)
+Message *Client::FindQueryById(uint16_t aMessageId)
 {
     uint16_t messageId;
     Message *message;
@@ -241,9 +256,8 @@ Message *Client::FindRelatedQuery(const Header &aResponseHeader, QueryMetadata &
             OT_ASSERT(false);
         }
 
-        if (HostSwap16(messageId) == aResponseHeader.GetMessageId())
+        if (HostSwap16(messageId) == aMessageId)
         {
-            aQueryMetadata.ReadFrom(*message);
             break;
         }
     }
@@ -346,7 +360,8 @@ void Client::HandleUdpReceive(Message &aMessage, const Ip6::MessageInfo &aMessag
     aMessage.MoveOffset(sizeof(responseHeader));
     offset = aMessage.GetOffset();
 
-    VerifyOrExit((message = FindRelatedQuery(responseHeader, queryMetadata)) != nullptr);
+    VerifyOrExit((message = FindQueryById(responseHeader.GetMessageId())) != nullptr);
+    queryMetadata.ReadFrom(*message);
 
     VerifyOrExit(responseHeader.GetResponseCode() == Header::kResponseSuccess, error = OT_ERROR_FAILED);
 
diff --git a/src/core/net/dns_client.hpp b/src/core/net/dns_client.hpp
index 4a491fe48..656f5c4f9 100644
--- a/src/core/net/dns_client.hpp
+++ b/src/core/net/dns_client.hpp
@@ -181,9 +181,11 @@ private:
     otError  SendMessage(Message &aMessage, const Ip6::MessageInfo &aMessageInfo);
     void     SendCopy(const Message &aMessage, const Ip6::MessageInfo &aMessageInfo);
 
+    otError GenerateUniqueRandomId(uint16_t &aRandomId);
+
     otError CompareQuestions(Message &aMessageResponse, Message &aMessageQuery, uint16_t &aOffset);
 
-    Message *FindRelatedQuery(const Header &aResponseHeader, QueryMetadata &aQueryMetadata);
+    Message *FindQueryById(uint16_t aMessageId);
     void     FinalizeDnsTransaction(Message &            aQuery,
                                     const QueryMetadata &aQueryMetadata,
                                     const Ip6::Address * aAddress,
@@ -198,7 +200,6 @@ private:
 
     Ip6::Udp::Socket mSocket;
 
-    uint16_t     mMessageId;
     MessageQueue mPendingQueries;
     TimerMilli   mRetransmissionTimer;
 };