Add 'nix daemon' command

4 files changed, 387 insertions, 0 deletions

diff --git a/src/nix/command.hh b/src/nix/command.hh
index 3aae57edd..f325cd906 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -13,6 +13,8 @@ namespace nix {
 
 extern std::string programPath;
 
+extern char * * savedArgv;
+
 class EvalState;
 struct Pos;
 class Store;
diff --git a/src/nix/daemon.cc b/src/nix/daemon.cc
new file mode 100644
index 000000000..204d4ce6b
--- /dev/null
+++ b/src/nix/daemon.cc
@@ -0,0 +1,361 @@
+#include "command.hh"
+#include "shared.hh"
+#include "local-store.hh"
+#include "remote-store.hh"
+#include "util.hh"
+#include "serialise.hh"
+#include "archive.hh"
+#include "globals.hh"
+#include "derivations.hh"
+#include "finally.hh"
+#include "../nix/legacy.hh"
+#include "daemon.hh"
+
+#include <algorithm>
+#include <climits>
+#include <cstring>
+
+#include <unistd.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <errno.h>
+#include <pwd.h>
+#include <grp.h>
+#include <fcntl.h>
+
+#if __APPLE__ || __FreeBSD__
+#include <sys/ucred.h>
+#endif
+
+using namespace nix;
+using namespace nix::daemon;
+
+#ifndef __linux__
+#define SPLICE_F_MOVE 0
+static ssize_t splice(int fd_in, void *off_in, int fd_out, void *off_out, size_t len, unsigned int flags)
+{
+    // We ignore most parameters, we just have them for conformance with the linux syscall
+    std::vector<char> buf(8192);
+    auto read_count = read(fd_in, buf.data(), buf.size());
+    if (read_count == -1)
+        return read_count;
+    auto write_count = decltype(read_count)(0);
+    while (write_count < read_count) {
+        auto res = write(fd_out, buf.data() + write_count, read_count - write_count);
+        if (res == -1)
+            return res;
+        write_count += res;
+    }
+    return read_count;
+}
+#endif
+
+
+static void sigChldHandler(int sigNo)
+{
+    // Ensure we don't modify errno of whatever we've interrupted
+    auto saved_errno = errno;
+    //  Reap all dead children.
+    while (waitpid(-1, 0, WNOHANG) > 0) ;
+    errno = saved_errno;
+}
+
+
+static void setSigChldAction(bool autoReap)
+{
+    struct sigaction act, oact;
+    act.sa_handler = autoReap ? sigChldHandler : SIG_DFL;
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(SIGCHLD, &act, &oact))
+        throw SysError("setting SIGCHLD handler");
+}
+
+
+bool matchUser(const string & user, const string & group, const Strings & users)
+{
+    if (find(users.begin(), users.end(), "*") != users.end())
+        return true;
+
+    if (find(users.begin(), users.end(), user) != users.end())
+        return true;
+
+    for (auto & i : users)
+        if (string(i, 0, 1) == "@") {
+            if (group == string(i, 1)) return true;
+            struct group * gr = getgrnam(i.c_str() + 1);
+            if (!gr) continue;
+            for (char * * mem = gr->gr_mem; *mem; mem++)
+                if (user == string(*mem)) return true;
+        }
+
+    return false;
+}
+
+
+struct PeerInfo
+{
+    bool pidKnown;
+    pid_t pid;
+    bool uidKnown;
+    uid_t uid;
+    bool gidKnown;
+    gid_t gid;
+};
+
+
+//  Get the identity of the caller, if possible.
+static PeerInfo getPeerInfo(int remote)
+{
+    PeerInfo peer = { false, 0, false, 0, false, 0 };
+
+#if defined(SO_PEERCRED)
+
+    ucred cred;
+    socklen_t credLen = sizeof(cred);
+    if (getsockopt(remote, SOL_SOCKET, SO_PEERCRED, &cred, &credLen) == -1)
+        throw SysError("getting peer credentials");
+    peer = { true, cred.pid, true, cred.uid, true, cred.gid };
+
+#elif defined(LOCAL_PEERCRED)
+
+#if !defined(SOL_LOCAL)
+#define SOL_LOCAL 0
+#endif
+
+    xucred cred;
+    socklen_t credLen = sizeof(cred);
+    if (getsockopt(remote, SOL_LOCAL, LOCAL_PEERCRED, &cred, &credLen) == -1)
+        throw SysError("getting peer credentials");
+    peer = { false, 0, true, cred.cr_uid, false, 0 };
+
+#endif
+
+    return peer;
+}
+
+
+#define SD_LISTEN_FDS_START 3
+
+
+static ref<Store> openUncachedStore()
+{
+    Store::Params params; // FIXME: get params from somewhere
+    // Disable caching since the client already does that.
+    params["path-info-cache-size"] = "0";
+    return openStore(settings.storeUri, params);
+}
+
+
+static void daemonLoop()
+{
+    if (chdir("/") == -1)
+        throw SysError("cannot change current directory");
+
+    //  Get rid of children automatically; don't let them become zombies.
+    setSigChldAction(true);
+
+    AutoCloseFD fdSocket;
+
+    //  Handle socket-based activation by systemd.
+    auto listenFds = getEnv("LISTEN_FDS");
+    if (listenFds) {
+        if (getEnv("LISTEN_PID") != std::to_string(getpid()) || listenFds != "1")
+            throw Error("unexpected systemd environment variables");
+        fdSocket = SD_LISTEN_FDS_START;
+        closeOnExec(fdSocket.get());
+    }
+
+    //  Otherwise, create and bind to a Unix domain socket.
+    else {
+        createDirs(dirOf(settings.nixDaemonSocketFile));
+        fdSocket = createUnixDomainSocket(settings.nixDaemonSocketFile, 0666);
+    }
+
+    //  Loop accepting connections.
+    while (1) {
+
+        try {
+            //  Accept a connection.
+            struct sockaddr_un remoteAddr;
+            socklen_t remoteAddrLen = sizeof(remoteAddr);
+
+            AutoCloseFD remote = accept(fdSocket.get(),
+                (struct sockaddr *) &remoteAddr, &remoteAddrLen);
+            checkInterrupt();
+            if (!remote) {
+                if (errno == EINTR) continue;
+                throw SysError("accepting connection");
+            }
+
+            closeOnExec(remote.get());
+
+            TrustedFlag trusted = NotTrusted;
+            PeerInfo peer = getPeerInfo(remote.get());
+
+            struct passwd * pw = peer.uidKnown ? getpwuid(peer.uid) : 0;
+            string user = pw ? pw->pw_name : std::to_string(peer.uid);
+
+            struct group * gr = peer.gidKnown ? getgrgid(peer.gid) : 0;
+            string group = gr ? gr->gr_name : std::to_string(peer.gid);
+
+            Strings trustedUsers = settings.trustedUsers;
+            Strings allowedUsers = settings.allowedUsers;
+
+            if (matchUser(user, group, trustedUsers))
+                trusted = Trusted;
+
+            if ((!trusted && !matchUser(user, group, allowedUsers)) || group == settings.buildUsersGroup)
+                throw Error("user '%1%' is not allowed to connect to the Nix daemon", user);
+
+            printInfo(format((string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""))
+                % (peer.pidKnown ? std::to_string(peer.pid) : "<unknown>")
+                % (peer.uidKnown ? user : "<unknown>"));
+
+            //  Fork a child to handle the connection.
+            ProcessOptions options;
+            options.errorPrefix = "unexpected Nix daemon error: ";
+            options.dieWithParent = false;
+            options.runExitHandlers = true;
+            options.allowVfork = false;
+            startProcess([&]() {
+                fdSocket = -1;
+
+                //  Background the daemon.
+                if (setsid() == -1)
+                    throw SysError("creating a new session");
+
+                //  Restore normal handling of SIGCHLD.
+                setSigChldAction(false);
+
+                //  For debugging, stuff the pid into argv[1].
+                if (peer.pidKnown && savedArgv[1]) {
+                    string processName = std::to_string(peer.pid);
+                    strncpy(savedArgv[1], processName.c_str(), strlen(savedArgv[1]));
+                }
+
+                //  Handle the connection.
+                FdSource from(remote.get());
+                FdSink to(remote.get());
+                processConnection(openUncachedStore(), from, to, trusted, NotRecursive, [&](Store & store) {
+#if 0
+                    /* Prevent users from doing something very dangerous. */
+                    if (geteuid() == 0 &&
+                        querySetting("build-users-group", "") == "")
+                        throw Error("if you run 'nix-daemon' as root, then you MUST set 'build-users-group'!");
+#endif
+                    store.createUser(user, peer.uid);
+                });
+
+                exit(0);
+            }, options);
+
+        } catch (Interrupted & e) {
+            return;
+        } catch (Error & error) {
+            ErrorInfo ei = error.info();
+            ei.hint = std::optional(hintfmt("error processing connection: %1%",
+                (error.info().hint.has_value() ? error.info().hint->str() : "")));
+            logError(ei);
+        }
+    }
+}
+
+static void runDaemon(bool stdio)
+{
+    if (stdio) {
+        if (auto store = openUncachedStore().dynamic_pointer_cast<RemoteStore>()) {
+            auto conn = store->openConnectionWrapper();
+            int from = conn->from.fd;
+            int to = conn->to.fd;
+
+            auto nfds = std::max(from, STDIN_FILENO) + 1;
+            while (true) {
+                fd_set fds;
+                FD_ZERO(&fds);
+                FD_SET(from, &fds);
+                FD_SET(STDIN_FILENO, &fds);
+                if (select(nfds, &fds, nullptr, nullptr, nullptr) == -1)
+                    throw SysError("waiting for data from client or server");
+                if (FD_ISSET(from, &fds)) {
+                    auto res = splice(from, nullptr, STDOUT_FILENO, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
+                    if (res == -1)
+                        throw SysError("splicing data from daemon socket to stdout");
+                    else if (res == 0)
+                        throw EndOfFile("unexpected EOF from daemon socket");
+                }
+                if (FD_ISSET(STDIN_FILENO, &fds)) {
+                    auto res = splice(STDIN_FILENO, nullptr, to, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
+                    if (res == -1)
+                        throw SysError("splicing data from stdin to daemon socket");
+                    else if (res == 0)
+                        return;
+                }
+            }
+        } else {
+            FdSource from(STDIN_FILENO);
+            FdSink to(STDOUT_FILENO);
+            /* Auth hook is empty because in this mode we blindly trust the
+               standard streams. Limiting access to those is explicitly
+               not `nix-daemon`'s responsibility. */
+            processConnection(openUncachedStore(), from, to, Trusted, NotRecursive, [&](Store & _){});
+        }
+    } else
+        daemonLoop();
+}
+
+static int main_nix_daemon(int argc, char * * argv)
+{
+    {
+        auto stdio = false;
+
+        parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
+            if (*arg == "--daemon")
+                ; //  ignored for backwards compatibility
+            else if (*arg == "--help")
+                showManPage("nix-daemon");
+            else if (*arg == "--version")
+                printVersion("nix-daemon");
+            else if (*arg == "--stdio")
+                stdio = true;
+            else return false;
+            return true;
+        });
+
+        initPlugins();
+
+        runDaemon(stdio);
+
+        return 0;
+    }
+}
+
+static RegisterLegacyCommand r_nix_daemon("nix-daemon", main_nix_daemon);
+
+struct CmdDaemon : StoreCommand
+{
+    std::string description() override
+    {
+        return "daemon to perform store operations on behalf of non-root clients";
+    }
+
+    Category category() override { return catUtility; }
+
+    std::string doc() override
+    {
+        return
+          #include "daemon.md"
+          ;
+    }
+
+    void run(ref<Store> store) override
+    {
+        runDaemon(false);
+    }
+};
+
+static auto rCmdDaemon = registerCommand2<CmdDaemon>({"daemon"});
diff --git a/src/nix/daemon.md b/src/nix/daemon.md
new file mode 100644
index 000000000..e97016a94
--- /dev/null
+++ b/src/nix/daemon.md
@@ -0,0 +1,21 @@
+R""(
+
+# Example
+
+* Run the daemon in the foreground:
+
+  ```console
+  # nix daemon
+  ```
+
+# Description
+
+This command runs the Nix daemon, which is a required component in
+multi-user Nix installations. It performs build actions and other
+operations on the Nix store on behalf of non-root users. Usually you
+don't run the daemon directly; instead it's managed by a service
+management framework such as `systemd`.
+
+Note that this daemon does not fork into the background.
+
+)""
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 398526020..418396280 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -52,6 +52,7 @@ static bool haveInternet()
 }
 
 std::string programPath;
+char * * savedArgv;
 
 struct NixArgs : virtual MultiCommand, virtual MixCommonArgs
 {
@@ -232,6 +233,8 @@ static auto rCmdHelp = registerCommand<CmdHelp>("help");
 
 void mainWrapped(int argc, char * * argv)
 {
+    savedArgv = argv;
+
     /* The chroot helper needs to be run before any threads have been
        started. */
     if (argc > 0 && argv[0] == chrootHelperName) {