nix-super/src/libmain/shared.cc

#include <iostream>
#include <cctype>

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include <pwd.h>
#include <grp.h>

extern "C" {
#include <aterm2.h>
}

#include "globals.hh"
#include "shared.hh"

#include "config.h"


volatile sig_atomic_t blockInt = 0;


void sigintHandler(int signo)
{
    if (!blockInt) {
        _isInterrupted = 1;
        blockInt = 1;
    }
}


void setLogType(string lt)
{
    if (lt == "pretty") logType = ltPretty;
    else if (lt == "escapes") logType = ltEscapes;
    else if (lt == "flat") logType = ltFlat;
    else throw UsageError("unknown log type");
}


void checkStoreNotSymlink(Path path)
{
    struct stat st;
    while (path.size()) {
        if (lstat(path.c_str(), &st))
            throw SysError(format("getting status of `%1%'") % path);
        if (S_ISLNK(st.st_mode))
            throw Error(format(
                "the path `%1%' is a symlink; "
                "this is not allowed for the Nix store and its parent directories")
                % path);
        path = dirOf(path);
    }
}


/* Initialize and reorder arguments, then call the actual argument
   processor. */
static void initAndRun(int argc, char * * argv)
{
    string root = getEnv("NIX_ROOT");
    if (root != "") {
        if (chroot(root.c_str()) != 0)
            throw SysError(format("changing root to `%1%'") % root);
    }
    
    /* Setup Nix paths. */
    nixStore = getEnv("NIX_STORE_DIR", canonPath(NIX_STORE_DIR));
    nixDataDir = getEnv("NIX_DATA_DIR", canonPath(NIX_DATA_DIR));
    nixLogDir = getEnv("NIX_LOG_DIR", canonPath(NIX_LOG_DIR));
    nixStateDir = getEnv("NIX_STATE_DIR", canonPath(NIX_STATE_DIR));
    nixDBPath = getEnv("NIX_DB_DIR", nixStateDir + "/db");

    /* Check that the store directory and its parent are not
       symlinks. */
    if (getEnv("NIX_IGNORE_SYMLINK_STORE") != "1")
        checkStoreNotSymlink(nixStore);

    /* Catch SIGINT. */
    struct sigaction act, oact;
    act.sa_handler = sigintHandler;
    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
    if (sigaction(SIGINT, &act, &oact))
        throw SysError("installing handler for SIGINT");

    /* Ignore SIGPIPE. */
    act.sa_handler = SIG_IGN;
    act.sa_flags = 0;
    if (sigaction(SIGPIPE, &act, &oact))
        throw SysError("ignoring SIGPIPE");

    /* Process the NIX_LOG_TYPE environment variable. */
    string lt = getEnv("NIX_LOG_TYPE");
    if (lt != "") setLogType(lt);

    /* Put the arguments in a vector. */
    Strings args, remaining;
    while (argc--) args.push_back(*argv++);
    args.erase(args.begin());
    
    /* Expand compound dash options (i.e., `-qlf' -> `-q -l -f'), and
       ignore options for the ATerm library. */
    for (Strings::iterator i = args.begin(); i != args.end(); ++i) {
        string arg = *i;
        if (string(arg, 0, 4) == "-at-") ;
        else if (arg.length() > 2 && arg[0] == '-' && arg[1] != '-') {
            for (unsigned int j = 1; j < arg.length(); j++)
                if (isalpha(arg[j]))
                    remaining.push_back((string) "-" + arg[j]);
                else {
                    remaining.push_back(string(arg, j));
                    break;
                }
        } else remaining.push_back(arg);
    }
    args = remaining;
    remaining.clear();

    /* Process default options. */
    for (Strings::iterator i = args.begin(); i != args.end(); ++i) {
        string arg = *i;
        if (arg == "--verbose" || arg == "-v")
            verbosity = (Verbosity) ((int) verbosity + 1);
        else if (arg == "--log-type") {
            ++i;
            if (i == args.end()) throw UsageError("`--log-type' requires an argument");
            setLogType(*i);
        }
        else if (arg == "--build-output" || arg == "-B")
            ; /* !!! obsolete - remove eventually */
        else if (arg == "--no-build-output" || arg == "-Q")
            buildVerbosity = lvlVomit;
        else if (arg == "--help") {
            printHelp();
            return;
        }
        else if (arg == "--version") {
            cout << format("%1% (Nix) %2%") % programId % NIX_VERSION << endl;
            return;
        }
        else if (arg == "--keep-failed" || arg == "-K")
            keepFailed = true;
        else if (arg == "--keep-going" || arg == "-k")
            keepGoing = true;
        else if (arg == "--fallback")
            tryFallback = true;
        else if (arg == "--max-jobs" || arg == "-j") {
            ++i;
            if (i == args.end()) throw UsageError("`--max-jobs' requires an argument");
            istringstream str(*i);
            int n;
            str >> n;
            if (!str || !str.eof() || n < 0)
                throw UsageError(format("`--max-jobs' requires a non-negative integer"));
            maxBuildJobs = n;
        }
        else remaining.push_back(arg);
    }

    run(remaining);
}


void switchToNixUser()
{
#if SETUID_HACK

    /* Here we set the uid and gid to the Nix user and group,
       respectively, IF the current (real) user is a member of the Nix
       group.  Otherwise we just drop all privileges. */
    
    /* Lookup the Nix gid. */
    struct group * gr = getgrnam(NIX_GROUP);
    if (!gr) {
        cerr << format("missing group `%1%'\n") % NIX_GROUP;
        exit(1);
    }

    /* Get the supplementary group IDs for the current user. */
    int maxGids = 512, nrGids;
    gid_t gids[maxGids];
    if ((nrGids = getgroups(maxGids, gids)) == -1) {
        cerr << format("unable to query gids\n");
        exit(1);
    }

    /* Check that the current user is a member of the Nix group. */
    bool found = false;
    for (int i = 0; i < nrGids; ++i)
        if (gids[i] == gr->gr_gid) {
            found = true;
            break;
        }

    if (!found) {
        /* Not in the Nix group - drop all root/Nix privileges. */
        setgid(getgid());
        setuid(getuid());
        return;
    }

    /* Set the real, effective and saved gids to gr->gr_gid.  Also
       make very sure that this succeeded.  We switch the gid first
       because we cannot do it after we have dropped root uid. */
    if (setgid(gr->gr_gid) != 0 ||
        getgid() != gr->gr_gid ||
        getegid() != gr->gr_gid)
    {
        cerr << format("unable to set gid to `%1%'\n") % NIX_GROUP;
        exit(1);
    }

    /* Lookup the Nix uid. */
    struct passwd * pw = getpwnam(NIX_USER);
    if (!pw) {
        cerr << format("missing user `%1%'\n") % NIX_USER;
        exit(1);
    }

    /* This will drop all root privileges, setting the real, effective
       and saved uids to pw->pw_uid.  Also make very sure that this
       succeeded.*/
    if (setuid(pw->pw_uid) != 0 ||
        getuid() != pw->pw_uid ||
        geteuid() != pw->pw_uid)
    {
        cerr << format("unable to set uid to `%1%'\n") % NIX_USER;
        exit(1);
    }

#endif
}


static char buf[1024];

int main(int argc, char * * argv)
{
    /* If we are setuid root, we have to get rid of the excess
       privileges ASAP. */
    printMsg(lvlError, format("%1% %2% %3% %4%\n") % getuid() % geteuid()
        % getgid() % getegid());
    switchToNixUser();
    printMsg(lvlError, format("%1% %2% %3% %4%\n") % getuid() % geteuid()
        % getgid() % getegid());
    
    /* ATerm setup. */
    ATerm bottomOfStack;
    ATinit(argc, argv, &bottomOfStack);

    /* Turn on buffering for cerr. */
#if HAVE_PUBSETBUF
    cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
#endif

    try {
        try {
            initAndRun(argc, argv);
        } catch (...) {
            /* Subtle: we have to make sure that any `interrupted'
               condition is discharged before we reach printMsg()
               below, since otherwise it will throw an (uncaught)
               exception. */
            blockInt = 1; /* ignore further SIGINTs */
            _isInterrupted = 0;
            throw;
        }
    } catch (UsageError & e) {
        printMsg(lvlError, 
            format(
                "error: %1%\n"
                "Try `%2% --help' for more information.")
            % e.what() % programId);
        return 1;
    } catch (Error & e) {
        printMsg(lvlError, format("error: %1%") % e.msg());
        return 1;
    } catch (exception & e) {
        printMsg(lvlError, format("error: %1%") % e.what());
        return 1;
    }

    return 0;
}