lix/src/nix-daemon/nix-daemon.cc

#include "shared.hh"
#include "local-store.hh"
#include "util.hh"
#include "serialise.hh"
#include "archive.hh"
#include "globals.hh"
#include "derivations.hh"
#include "finally.hh"
#include "legacy.hh"
#include "daemon.hh"

#include <algorithm>

#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>
#include <limits.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 void daemonLoop(char * * argv)
{
    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. */
    if (getEnv("LISTEN_FDS") != "") {
        if (getEnv("LISTEN_PID") != std::to_string(getpid()) || getEnv("LISTEN_FDS") != "1")
            throw Error("unexpected systemd environment variables");
        fdSocket = SD_LISTEN_FDS_START;
    }

    /* Otherwise, create and bind to a Unix domain socket. */
    else {

        /* Create and bind to a Unix domain socket. */
        fdSocket = socket(PF_UNIX, SOCK_STREAM, 0);
        if (!fdSocket)
            throw SysError("cannot create Unix domain socket");

        string socketPath = settings.nixDaemonSocketFile;

        createDirs(dirOf(socketPath));

        /* Urgh, sockaddr_un allows path names of only 108 characters.
           So chdir to the socket directory so that we can pass a
           relative path name. */
        if (chdir(dirOf(socketPath).c_str()) == -1)
            throw SysError("cannot change current directory");
        Path socketPathRel = "./" + baseNameOf(socketPath);

        struct sockaddr_un addr;
        addr.sun_family = AF_UNIX;
        if (socketPathRel.size() >= sizeof(addr.sun_path))
            throw Error(format("socket path '%1%' is too long") % socketPathRel);
        strcpy(addr.sun_path, socketPathRel.c_str());

        unlink(socketPath.c_str());

        /* Make sure that the socket is created with 0666 permission
           (everybody can connect --- provided they have access to the
           directory containing the socket). */
        mode_t oldMode = umask(0111);
        int res = bind(fdSocket.get(), (struct sockaddr *) &addr, sizeof(addr));
        umask(oldMode);
        if (res == -1)
            throw SysError(format("cannot bind to socket '%1%'") % socketPath);

        if (chdir("/") == -1) /* back to the root */
            throw SysError("cannot change current directory");

        if (listen(fdSocket.get(), 5) == -1)
            throw SysError(format("cannot listen on socket '%1%'") % socketPath);
    }

    closeOnExec(fdSocket.get());

    /* 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());

            bool trusted = false;
            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 = true;

            if ((!trusted && !matchUser(user, group, allowedUsers)) || group == settings.buildUsersGroup)
                throw Error(format("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(format("creating a new session"));

                /* Restore normal handling of SIGCHLD. */
                setSigChldAction(false);

                /* For debugging, stuff the pid into argv[1]. */
                if (peer.pidKnown && argv[1]) {
                    string processName = std::to_string(peer.pid);
                    strncpy(argv[1], processName.c_str(), strlen(argv[1]));
                }

                /* Handle the connection. */
                FdSource from(remote.get());
                FdSink to(remote.get());
                processConnection(from, to, trusted, user, peer.uid);

                exit(0);
            }, options);

        } catch (Interrupted & e) {
            return;
        } catch (Error & e) {
            printError(format("error processing connection: %1%") % e.msg());
        }
    }
}


static int _main(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();

        if (stdio) {
            if (getStoreType() == tDaemon) {
                /* Forward on this connection to the real daemon */
                auto socketPath = settings.nixDaemonSocketFile;
                auto s = socket(PF_UNIX, SOCK_STREAM, 0);
                if (s == -1)
                    throw SysError("creating Unix domain socket");

                auto socketDir = dirOf(socketPath);
                if (chdir(socketDir.c_str()) == -1)
                    throw SysError(format("changing to socket directory '%1%'") % socketDir);

                auto socketName = baseNameOf(socketPath);
                auto addr = sockaddr_un{};
                addr.sun_family = AF_UNIX;
                if (socketName.size() + 1 >= sizeof(addr.sun_path))
                    throw Error(format("socket name %1% is too long") % socketName);
                strcpy(addr.sun_path, socketName.c_str());

                if (connect(s, (struct sockaddr *) &addr, sizeof(addr)) == -1)
                    throw SysError(format("cannot connect to daemon at %1%") % socketPath);

                auto nfds = (s > STDIN_FILENO ? s : STDIN_FILENO) + 1;
                while (true) {
                    fd_set fds;
                    FD_ZERO(&fds);
                    FD_SET(s, &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(s, &fds)) {
                        auto res = splice(s, 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, s, nullptr, SSIZE_MAX, SPLICE_F_MOVE);
                        if (res == -1)
                            throw SysError("splicing data from stdin to daemon socket");
                        else if (res == 0)
                            return 0;
                    }
                }
            } else {
                FdSource from(STDIN_FILENO);
                FdSink to(STDOUT_FILENO);
                processConnection(from, to, true, "root", 0);
            }
        } else {
            daemonLoop(argv);
        }

        return 0;
    }
}

static RegisterLegacyCommand s1("nix-daemon", _main);