Merge pull request #8230 from obsidiansystems/daemon-trust-override

Experimentally allow forcing `nix-daemon` trust; use this to test

src/libstore/daemon.cc

@@ -1067,6 +1067,8 @@ void processConnection(
 
             opCount++;
 
+            debug("performing daemon worker op: %d", op);
+
             try {
                 performOp(tunnelLogger, store, trusted, recursive, clientVersion, from, to, op);
             } catch (Error & e) {

src/libutil/experimental-features.cc

@@ -12,7 +12,7 @@ struct ExperimentalFeatureDetails
     std::string_view description;
 };
 
-constexpr std::array<ExperimentalFeatureDetails, 11> xpFeatureDetails = {{
+constexpr std::array<ExperimentalFeatureDetails, 12> xpFeatureDetails = {{
     {
         .tag = Xp::CaDerivations,
         .name = "ca-derivations",
@@ -189,6 +189,16 @@ constexpr std::array<ExperimentalFeatureDetails, 11> xpFeatureDetails = {{
             runtime dependencies.
         )",
     },
+    {
+        .tag = Xp::DaemonTrustOverride,
+        .name = "daemon-trust-override",
+        .description = R"(
+            Allow forcing trusting or not trusting clients with
+            `nix-daemon`. This is useful for testing, but possibly also
+            useful for various experiments with `nix-daemon --stdio`
+            networking.
+        )",
+    },
 }};
 
 static_assert(

src/libutil/experimental-features.hh

@@ -28,6 +28,7 @@ enum struct ExperimentalFeature
     AutoAllocateUids,
     Cgroups,
     DiscardReferences,
+    DaemonTrustOverride,
 };
 
 /**

src/nix/daemon.cc

@@ -273,8 +273,12 @@ static std::pair<TrustedFlag, std::string> authPeer(const PeerInfo & peer)
 /**
  * Run a server. The loop opens a socket and accepts new connections from that
  * socket.
+ *
+ * @param forceTrustClientOpt If present, force trusting or not trusted
+ * the client. Otherwise, decide based on the authentication settings
+ * and user credentials (from the unix domain socket).
  */
-static void daemonLoop()
+static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
 {
     if (chdir("/") == -1)
         throw SysError("cannot change current directory");
@@ -317,9 +321,18 @@ static void daemonLoop()
 
             closeOnExec(remote.get());
 
-            PeerInfo peer = getPeerInfo(remote.get());
+            PeerInfo peer { .pidKnown = false };
-            auto [_trusted, user] = authPeer(peer);
+            TrustedFlag trusted;
-            auto trusted = _trusted;
+            std::string user;
+
+            if (forceTrustClientOpt)
+                trusted = *forceTrustClientOpt;
+            else {
+                peer = getPeerInfo(remote.get());
+                auto [_trusted, _user] = authPeer(peer);
+                trusted = _trusted;
+                user = _user;
+            };
 
             printInfo((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""),
                 peer.pidKnown ? std::to_string(peer.pid) : "<unknown>",
@@ -410,38 +423,47 @@ static void forwardStdioConnection(RemoteStore & store) {
  * Unlike `forwardStdioConnection()` we do process commands ourselves in
  * this case, not delegating to another daemon.
  *
- * @note `Trusted` is unconditionally passed because in this mode we
+ * @param trustClient Whether to trust the client. Forwarded directly to
- * blindly trust the standard streams. Limiting access to those is
+ * `processConnection()`.
- * explicitly not `nix-daemon`'s responsibility.
  */
-static void processStdioConnection(ref<Store> store)
+static void processStdioConnection(ref<Store> store, TrustedFlag trustClient)
 {
     FdSource from(STDIN_FILENO);
     FdSink to(STDOUT_FILENO);
-    processConnection(store, from, to, Trusted, NotRecursive);
+    processConnection(store, from, to, trustClient, NotRecursive);
 }
 
 /**
  * Entry point shared between the new CLI `nix daemon` and old CLI
  * `nix-daemon`.
+ *
+ * @param forceTrustClientOpt See `daemonLoop()` and the parameter with
+ * the same name over there for details.
  */
-static void runDaemon(bool stdio)
+static void runDaemon(bool stdio, std::optional<TrustedFlag> forceTrustClientOpt)
 {
     if (stdio) {
         auto store = openUncachedStore();
 
-        if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>())
+        // If --force-untrusted is passed, we cannot forward the connection and
+        // must process it ourselves (before delegating to the next store) to
+        // force untrusting the client.
+        if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>(); remoteStore && (!forceTrustClientOpt || *forceTrustClientOpt != NotTrusted))
             forwardStdioConnection(*remoteStore);
         else
-            processStdioConnection(store);
+            // `Trusted` is passed in the auto (no override case) because we
+            // cannot see who is on the other side of a plain pipe. Limiting
+            // access to those is explicitly not `nix-daemon`'s responsibility.
+            processStdioConnection(store, forceTrustClientOpt.value_or(Trusted));
     } else
-        daemonLoop();
+        daemonLoop(forceTrustClientOpt);
 }
 
 static int main_nix_daemon(int argc, char * * argv)
 {
     {
         auto stdio = false;
+        std::optional<TrustedFlag> isTrustedOpt = std::nullopt;
 
         parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--daemon")
@@ -452,11 +474,20 @@ static int main_nix_daemon(int argc, char * * argv)
                 printVersion("nix-daemon");
             else if (*arg == "--stdio")
                 stdio = true;
-            else return false;
+            else if (*arg == "--force-trusted") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = Trusted;
+            } else if (*arg == "--force-untrusted") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = NotTrusted;
+            } else if (*arg == "--default-trust") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = std::nullopt;
+            } else return false;
             return true;
         });
 
-        runDaemon(stdio);
+        runDaemon(stdio, isTrustedOpt);
 
         return 0;
     }
@@ -482,7 +513,7 @@ struct CmdDaemon : StoreCommand
 
     void run(ref<Store> store) override
     {
-        runDaemon(false);
+        runDaemon(false, std::nullopt);
     }
 };
 

tests/build-remote-trustless-after.sh

@@ -0,0 +1,2 @@
+outPath=$(readlink -f $TEST_ROOT/result)
+grep 'FOO BAR BAZ' ${remoteDir}/${outPath}

tests/build-remote-trustless-should-fail-0.sh

@@ -0,0 +1,29 @@
+source common.sh
+
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+# We first build a dependency of the derivation we eventually want to
+# build.
+nix-build build-hook.nix -A passthru.input2 \
+  -o "$TEST_ROOT/input2" \
+  --arg busybox "$busybox" \
+  --store "$TEST_ROOT/local" \
+  --option system-features bar
+
+# Now when we go to build that downstream derivation, Nix will fail
+# because we cannot trustlessly build input-addressed derivations with
+# `inputDrv` dependencies.
+
+file=build-hook.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+
+expectStderr 1 source build-remote-trustless.sh \
+    | grepQuiet "you are not privileged to build input-addressed derivations"

tests/build-remote-trustless-should-pass-0.sh

@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us
+file=build-hook.nix
+prog=nix-store
+proto=ssh
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless-should-pass-1.sh

@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us
+file=build-hook.nix
+prog=nix-daemon
+proto=ssh-ng
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless-should-pass-3.sh

@@ -0,0 +1,14 @@
+source common.sh
+
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
+# Remote doesn't trusts us, but this is fine because we are only
+# building (fixed) CA derivations.
+file=build-hook-ca-fixed.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless.sh

@@ -0,0 +1,14 @@
+requireSandboxSupport
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+remoteDir=$TEST_ROOT/remote
+
+# Note: ssh{-ng}://localhost bypasses ssh. See tests/build-remote.sh for
+# more details.
+nix-build $file -o $TEST_ROOT/result --max-jobs 0 \
+  --arg busybox $busybox \
+  --store $TEST_ROOT/local \
+  --builders "$proto://localhost?remote-program=$prog&remote-store=${remoteDir}%3Fsystem-features=foo%20bar%20baz - - 1 1 foo,bar,baz"

tests/local.mk

@@ -70,6 +70,10 @@ nix_tests = \
   check-reqs.sh \
   build-remote-content-addressed-fixed.sh \
   build-remote-content-addressed-floating.sh \
+  build-remote-trustless-should-pass-0.sh \
+  build-remote-trustless-should-pass-1.sh \
+  build-remote-trustless-should-pass-3.sh \
+  build-remote-trustless-should-fail-0.sh \
   nar-access.sh \
   pure-eval.sh \
   eval.sh \

tests/nix-daemon-untrusting.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec nix-daemon --force-untrusted "$@"