add dns hosts file option for user side dns filtering

llarp/config/config.cpp

@@ -748,6 +748,21 @@ namespace llarp
             m_bind.setPort(53);
         });
 
+    conf.defineOption<std::string>(
+        "dns",
+        "add-hosts",
+        ClientOnly,
+        Comment{"Add a hosts file to the dns resolver", "For use with client side dns filtering"},
+        [=](std::string arg) {
+          if (arg.empty())
+            return;
+          fs::path path{arg};
+          if (not exists(path))
+            throw std::invalid_argument{
+                stringify("cannot add hosts file ", path, " as it does not seem to exist")};
+          m_hostfiles.emplace_back(std::move(path));
+        });
+
     // Ignored option (used by the systemd service file to disable resolvconf configuration).
     conf.defineOption<bool>(
         "dns",

llarp/config/config.hpp

@@ -137,6 +137,7 @@ namespace llarp
   {
     SockAddr m_bind;
     std::vector<SockAddr> m_upstreamDNS;
+    std::vector<fs::path> m_hostfiles;
 
     void
     defineConfigOptions(ConfigDefinition& conf, const ConfigGenParameters& params);

llarp/dns/server.cpp

@@ -26,9 +26,9 @@ namespace llarp::dns
   }
 
   bool
-  Proxy::Start(SockAddr addr, std::vector<SockAddr> resolvers)
+  Proxy::Start(SockAddr addr, std::vector<SockAddr> resolvers, std::vector<fs::path> hostfiles)
   {
-    if (not PacketHandler::Start(addr, std::move(resolvers)))
+    if (not PacketHandler::Start(addr, std::move(resolvers), std::move(hostfiles)))
       return false;
     return m_Server->listen(addr);
   }
@@ -44,13 +44,14 @@ namespace llarp::dns
   }
 
   bool
-  PacketHandler::Start(SockAddr, std::vector<SockAddr> resolvers)
+  PacketHandler::Start(SockAddr, std::vector<SockAddr> resolvers, std::vector<fs::path> hostfiles)
   {
-    return SetupUnboundResolver(std::move(resolvers));
+    return SetupUnboundResolver(std::move(resolvers), std::move(hostfiles));
   }
 
   bool
-  PacketHandler::SetupUnboundResolver(std::vector<SockAddr> resolvers)
+  PacketHandler::SetupUnboundResolver(
+      std::vector<SockAddr> resolvers, std::vector<fs::path> hostfiles)
   {
     // if we have no resolvers don't set up unbound
     if (resolvers.empty())
@@ -85,6 +86,10 @@ namespace llarp::dns
       }
       m_Resolvers.emplace(resolver);
     }
+    for (const auto& path : hostfiles)
+    {
+      m_UnboundResolver->AddHostsFile(path);
+    }
 
     return true;
   }

llarp/dns/server.hpp

@@ -35,7 +35,10 @@ namespace llarp
       virtual ~PacketHandler() = default;
 
       virtual bool
-      Start(SockAddr localaddr, std::vector<SockAddr> upstreamResolvers);
+      Start(
+          SockAddr localaddr,
+          std::vector<SockAddr> upstreamResolvers,
+          std::vector<fs::path> hostfiles);
 
       void
       Stop();
@@ -58,7 +61,7 @@ namespace llarp
       HandleUpstreamFailure(const SockAddr& from, const SockAddr& to, Message msg);
 
       bool
-      SetupUnboundResolver(std::vector<SockAddr> resolvers);
+      SetupUnboundResolver(std::vector<SockAddr> resolvers, std::vector<fs::path> hostfiles);
 
       IQueryHandler* const m_QueryHandler;
       std::set<SockAddr> m_Resolvers;
@@ -73,7 +76,10 @@ namespace llarp
       explicit Proxy(EventLoop_ptr loop, IQueryHandler* handler);
 
       bool
-      Start(SockAddr localaddr, std::vector<SockAddr> resolvers) override;
+      Start(
+          SockAddr localaddr,
+          std::vector<SockAddr> upstreamResolvers,
+          std::vector<fs::path> hostfiles) override;
 
      protected:
       void

llarp/dns/unbound_resolver.cpp

@@ -3,6 +3,7 @@
 #include "server.hpp"
 #include <llarp/util/buffer.hpp>
 #include <sstream>
+#include <llarp/util/str.hpp>
 
 namespace llarp::dns
 {
@@ -119,6 +120,21 @@ namespace llarp::dns
     return true;
   }
 
+  void
+  UnboundResolver::AddHostsFile(const fs::path& file)
+  {
+    LogDebug("adding hosts file ", file);
+    const auto str = file.u8string();
+    if (auto ret = ub_ctx_hosts(unboundContext, str.c_str()))
+    {
+      throw std::runtime_error{stringify("Failed to add host file ", file, ": ", ub_strerror(ret))};
+    }
+    else
+    {
+      LogInfo("added hosts file ", file);
+    }
+  }
+
   void
   UnboundResolver::Lookup(SockAddr to, SockAddr from, Message msg)
   {

llarp/dns/unbound_resolver.hpp

@@ -7,6 +7,7 @@
 #include <queue>
 
 #include <llarp/ev/ev.hpp>
+#include <llarp/util/fs.hpp>
 
 #include "message.hpp"
 
@@ -52,6 +53,9 @@ namespace llarp::dns
     bool
     AddUpstreamResolver(const SockAddr& upstreamResolverIP);
 
+    void
+    AddHostsFile(const fs::path& file);
+
     void
     Lookup(SockAddr to, SockAddr from, Message msg);
   };

llarp/handlers/exit.cpp

@@ -477,7 +477,7 @@ namespace llarp
         GetRouter()->loop()->add_ticker([this] { Flush(); });
 
         llarp::LogInfo("Trying to start resolver ", m_LocalResolverAddr);
-        return m_Resolver->Start(m_LocalResolverAddr, m_UpstreamResolvers);
+        return m_Resolver->Start(m_LocalResolverAddr, m_UpstreamResolvers, {});
       }
       return true;
     }

llarp/handlers/tun.cpp

@@ -169,6 +169,7 @@ namespace llarp
 
       m_LocalResolverAddr = dnsConf.m_bind;
       m_UpstreamResolvers = dnsConf.m_upstreamDNS;
+      m_hostfiles = dnsConf.m_hostfiles;
 
       m_BaseV6Address = conf.m_baseV6Address;
 
@@ -945,7 +946,8 @@ namespace llarp
         llarp::LogError(Name(), " failed to set up network interface");
         return false;
       }
-      if (!m_Resolver->Start(m_LocalResolverAddr.createSockAddr(), m_UpstreamResolvers))
+      if (!m_Resolver->Start(
+              m_LocalResolverAddr.createSockAddr(), m_UpstreamResolvers, m_hostfiles))
       {
         llarp::LogError(Name(), " failed to start DNS server");
         return false;

llarp/handlers/tun.hpp

@@ -266,6 +266,8 @@ namespace llarp
       llarp::IPRange m_OurRange;
       /// upstream dns resolver list
       std::vector<SockAddr> m_UpstreamResolvers;
+      /// dns host files list
+      std::vector<fs::path> m_hostfiles;
       /// local dns
       IpAddress m_LocalResolverAddr;
       /// list of strict connect addresses for hooks