path: root/src/libutil/util.cc

#include "config.h"

#ifdef __CYGWIN__
#include <windows.h>
#endif

#include <iostream>
#include <cerrno>
#include <cstdio>
#include <sstream>

#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>

#include <sys/types.h>
#include <pwd.h>
#include <grp.h>

#include "util.hh"


namespace nix {


Error::Error(const format & f)
{
    err = f.str();
}


Error & Error::addPrefix(const format & f)
{
    err = f.str() + err;
    return *this;
}


SysError::SysError(const format & f)
    : Error(format("%1%: %2%") % f.str() % strerror(errno))
{
}


string getEnv(const string & key, const string & def)
{
    char * value = getenv(key.c_str());
    return value ? string(value) : def;
}


Path absPath(Path path, Path dir)
{
    if (path[0] != '/') {
        if (dir == "") {
            char buf[PATH_MAX];
            if (!getcwd(buf, sizeof(buf)))
                throw SysError("cannot get cwd");
            dir = buf;
        }
        path = dir + "/" + path;
    }
    return canonPath(path);
}


Path canonPath(const Path & path, bool resolveSymlinks)
{
    string s;

    if (path[0] != '/')
        throw Error(format("not an absolute path: `%1%'") % path);

    string::const_iterator i = path.begin(), end = path.end();
    string temp;

    /* Count the number of times we follow a symlink and stop at some
       arbitrary (but high) limit to prevent infinite loops. */
    unsigned int followCount = 0, maxFollow = 1024;

    while (1) {

        /* Skip slashes. */
        while (i != end && *i == '/') i++;
        if (i == end) break;

        /* Ignore `.'. */
        if (*i == '.' && (i + 1 == end || i[1] == '/'))
            i++;

        /* If `..', delete the last component. */
        else if (*i == '.' && i + 1 < end && i[1] == '.' && 
            (i + 2 == end || i[2] == '/'))
        {
            if (!s.empty()) s.erase(s.rfind('/'));
            i += 2;
        }

        /* Normal component; copy it. */
        else {
            s += '/';
            while (i != end && *i != '/') s += *i++;

            /* If s points to a symlink, resolve it and restart (since
               the symlink target might contain new symlinks). */
            if (resolveSymlinks && isLink(s)) {
                followCount++;
                if (followCount >= maxFollow)
                    throw Error(format("infinite symlink recursion in path `%1%'") % path);
                temp = absPath(readLink(s), dirOf(s))
                    + string(i, end);
                i = temp.begin(); /* restart */
                end = temp.end();
                s = "";
                /* !!! potential for infinite loop */
            }
        }
    }

    return s.empty() ? "/" : s;
}


Path dirOf(const Path & path)
{
    Path::size_type pos = path.rfind('/');
    if (pos == string::npos)
        throw Error(format("invalid file name: %1%") % path);
    return pos == 0 ? "/" : Path(path, 0, pos);
}


string baseNameOf(const Path & path)
{
    Path::size_type pos = path.rfind('/');
    if (pos == string::npos)
        throw Error(format("invalid file name %1% ") % path);
    return string(path, pos + 1);
}


bool pathExists(const Path & path)
{
    int res;
    struct stat st;
    res = lstat(path.c_str(), &st);
    if (!res) return true;
    if (errno != ENOENT && errno != ENOTDIR)
        throw SysError(format("getting status of %1%") % path);
    return false;
}


Path readLink(const Path & path)
{
    struct stat st;
    if (lstat(path.c_str(), &st))
        throw SysError(format("getting status of `%1%'") % path);
    if (!S_ISLNK(st.st_mode))
        throw Error(format("`%1%' is not a symlink") % path);
    char buf[st.st_size];
    if (readlink(path.c_str(), buf, st.st_size) != st.st_size)
        throw SysError(format("reading symbolic link `%1%'") % path);
    return string(buf, st.st_size);
}


bool isLink(const Path & path)
{
    struct stat st;
    if (lstat(path.c_str(), &st))
        throw SysError(format("getting status of `%1%'") % path);
    return S_ISLNK(st.st_mode);
}


Strings readDirectory(const Path & path)
{
    Strings names;

    AutoCloseDir dir = opendir(path.c_str());
    if (!dir) throw SysError(format("opening directory `%1%'") % path);

    struct dirent * dirent;
    while (errno = 0, dirent = readdir(dir)) { /* sic */
        checkInterrupt();
        string name = dirent->d_name;
        if (name == "." || name == "..") continue;
        names.push_back(name);
    }
    if (errno) throw SysError(format("reading directory `%1%'") % path);

    return names;
}


template <class T>
struct AutoDeleteArray
{
    T * p;
    AutoDeleteArray(T * p) : p(p) { }
    ~AutoDeleteArray() 
    {
        delete [] p;
    }
};


string readFile(int fd)
{
    struct stat st;
    if (fstat(fd, &st) == -1)
        throw SysError("statting file");
    
    unsigned char * buf = new unsigned char[st.st_size];
    AutoDeleteArray<unsigned char> d(buf);
    readFull(fd, buf, st.st_size);

    return string((char *) buf, st.st_size);
}


string readFile(const Path & path)
{
    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
    if (fd == -1)
        throw SysError(format("opening file `%1%'") % path);
    return readFile(fd);
}


void writeFile(const Path & path, const string & s)
{
    AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
    if (fd == -1)
        throw SysError(format("opening file `%1%'") % path);
    writeFull(fd, (unsigned char *) s.c_str(), s.size());
}


unsigned long long computePathSize(const Path & path)
{
    unsigned long long size = 0;
    
    checkInterrupt();

    struct stat st;
    if (lstat(path.c_str(), &st))
	throw SysError(format("getting attributes of path `%1%'") % path);

    size += st.st_size;

    if (S_ISDIR(st.st_mode)) {
	Strings names = readDirectory(path);

	for (Strings::iterator i = names.begin(); i != names.end(); ++i)
            size += computePathSize(path + "/" + *i);
    }

    return size;
}


static void _deletePath(const Path & path, unsigned long long & bytesFreed)
{
    checkInterrupt();

    printMsg(lvlVomit, format("%1%") % path);

    struct stat st;
    if (lstat(path.c_str(), &st))
	throw SysError(format("getting attributes of path `%1%'") % path);

    bytesFreed += st.st_size;

    if (S_ISDIR(st.st_mode)) {
	Strings names = readDirectory(path);

	/* Make the directory writable. */
	if (!(st.st_mode & S_IWUSR)) {
	    if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
		throw SysError(format("making `%1%' writable") % path);
	}

	for (Strings::iterator i = names.begin(); i != names.end(); ++i)
            _deletePath(path + "/" + *i, bytesFreed);
    }

    if (remove(path.c_str()) == -1)
        throw SysError(format("cannot unlink `%1%'") % path);
}


void deletePath(const Path & path)
{
    unsigned long long dummy;
    deletePath(path, dummy);
}


void deletePath(const Path & path, unsigned long long & bytesFreed)
{
    startNest(nest, lvlDebug,
        format("recursively deleting path `%1%'") % path);
    bytesFreed = 0;
    _deletePath(path, bytesFreed);
}


void makePathReadOnly(const Path & path)
{
    checkInterrupt();

    struct stat st;
    if (lstat(path.c_str(), &st))
	throw SysError(format("getting attributes of path `%1%'") % path);

    if (!S_ISLNK(st.st_mode) && (st.st_mode & S_IWUSR)) {
	if (chmod(path.c_str(), st.st_mode & ~S_IWUSR) == -1)
	    throw SysError(format("making `%1%' read-only") % path);
    }

    if (S_ISDIR(st.st_mode)) {
        Strings names = readDirectory(path);
	for (Strings::iterator i = names.begin(); i != names.end(); ++i)
	    makePathReadOnly(path + "/" + *i);
    }
}


static Path tempName()
{
    static int counter = 0;
    Path tmpRoot = canonPath(getEnv("TMPDIR", "/tmp"), true);
    return (format("%1%/nix-%2%-%3%") % tmpRoot % getpid() % counter++).str();
}


Path createTempDir()
{
    while (1) {
        checkInterrupt();
	Path tmpDir = tempName();
	if (mkdir(tmpDir.c_str(), 0777) == 0) {
	    /* Explicitly set the group of the directory.  This is to
	       work around around problems caused by BSD's group
	       ownership semantics (directories inherit the group of
	       the parent).  For instance, the group of /tmp on
	       FreeBSD is "wheel", so all directories created in /tmp
	       will be owned by "wheel"; but if the user is not in
	       "wheel", then "tar" will fail to unpack archives that
	       have the setgid bit set on directories. */
	    if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
		throw SysError(format("setting group of directory `%1%'") % tmpDir);
	    return tmpDir;
	}
	if (errno != EEXIST)
	    throw SysError(format("creating directory `%1%'") % tmpDir);
    }
}


void createDirs(const Path & path)
{
    if (path == "/") return;
    createDirs(dirOf(path));
    if (!pathExists(path))
        if (mkdir(path.c_str(), 0777) == -1)
            throw SysError(format("creating directory `%1%'") % path);
}


void writeStringToFile(const Path & path, const string & s)
{
    AutoCloseFD fd(open(path.c_str(),
        O_CREAT | O_EXCL | O_WRONLY, 0666));
    if (fd == -1)
        throw SysError(format("creating file `%1%'") % path);
    writeFull(fd, (unsigned char *) s.c_str(), s.size());
}


LogType logType = ltPretty;
Verbosity verbosity = lvlInfo;

static int nestingLevel = 0;


Nest::Nest()
{
    nest = false;
}


Nest::~Nest()
{
    close();
}


static string escVerbosity(Verbosity level)
{
    return int2String((int) level);
}


void Nest::open(Verbosity level, const format & f)
{
    if (level <= verbosity) {
        if (logType == ltEscapes)
            std::cerr << "\033[" << escVerbosity(level) << "p"
                      << f.str() << "\n";
        else
            printMsg_(level, f);
        nest = true;
        nestingLevel++;
    }
}


void Nest::close()
{
    if (nest) {
        nestingLevel--;
        if (logType == ltEscapes)
            std::cerr << "\033[q";
        nest = false;
    }
}


void printMsg_(Verbosity level, const format & f)
{
    checkInterrupt();
    if (level > verbosity) return;
    string prefix;
    if (logType == ltPretty)
        for (int i = 0; i < nestingLevel; i++)
            prefix += "|   ";
    else if (logType == ltEscapes && level != lvlInfo)
        prefix = "\033[" + escVerbosity(level) + "s";
    string s = (format("%1%%2%\n") % prefix % f.str()).str();
    writeFull(STDERR_FILENO, (const unsigned char *) s.c_str(), s.size());
}


void warnOnce(bool & haveWarned, const format & f)
{
    if (!haveWarned) {
        printMsg(lvlError, format("warning: %1%") % f.str());
        haveWarned = true;
    }
}


void readFull(int fd, unsigned char * buf, size_t count)
{
    while (count) {
        checkInterrupt();
        ssize_t res = read(fd, (char *) buf, count);
        if (res == -1) {
            if (errno == EINTR) continue;
            throw SysError("reading from file");
        }
        if (res == 0) throw Error("unexpected end-of-file");
        count -= res;
        buf += res;
    }
}


void writeFull(int fd, const unsigned char * buf, size_t count)
{
    while (count) {
        checkInterrupt();
        ssize_t res = write(fd, (char *) buf, count);
        if (res == -1) {
            if (errno == EINTR) continue;
            throw SysError("writing to file");
        }
        count -= res;
        buf += res;
    }
}


string drainFD(int fd)
{
    string result;
    unsigned char buffer[4096];
    while (1) {
        ssize_t rd = read(fd, buffer, sizeof buffer);
        if (rd == -1) {
            if (errno != EINTR)
                throw SysError("reading from file");
        }
        else if (rd == 0) break;
        else result.append((char *) buffer, rd);
    }
    return result;
}



//////////////////////////////////////////////////////////////////////


AutoDelete::AutoDelete(const string & p) : path(p)
{
    del = true;
}

AutoDelete::~AutoDelete()
{
    if (del) deletePath(path);
}

void AutoDelete::cancel()
{
    del = false;
}



//////////////////////////////////////////////////////////////////////


AutoCloseFD::AutoCloseFD()
{
    fd = -1;
}


AutoCloseFD::AutoCloseFD(int fd)
{
    this->fd = fd;
}


AutoCloseFD::AutoCloseFD(const AutoCloseFD & fd)
{
    abort();
}


AutoCloseFD::~AutoCloseFD()
{
    try {
        close();
    } catch (Error & e) {
        printMsg(lvlError, format("error (ignored): %1%") % e.msg());
    }
}


void AutoCloseFD::operator =(int fd)
{
    if (this->fd != fd) close();
    this->fd = fd;
}


AutoCloseFD::operator int() const
{
    return fd;
}


void AutoCloseFD::close()
{
    if (fd != -1) {
        if (::close(fd) == -1)
            /* This should never happen. */
            throw SysError("closing file descriptor");
        fd = -1;
    }
}


bool AutoCloseFD::isOpen()
{
    return fd != -1;
}


/* Pass responsibility for closing this fd to the caller. */
int AutoCloseFD::borrow()
{
    int oldFD = fd;
    fd = -1;
    return oldFD;
}


void Pipe::create()
{
    int fds[2];
    if (pipe(fds) != 0) throw SysError("creating pipe");
    readSide = fds[0];
    writeSide = fds[1];
}



//////////////////////////////////////////////////////////////////////


AutoCloseDir::AutoCloseDir()
{
    dir = 0;
}


AutoCloseDir::AutoCloseDir(DIR * dir)
{
    this->dir = dir;
}


AutoCloseDir::~AutoCloseDir()
{
    if (dir) closedir(dir);
}


void AutoCloseDir::operator =(DIR * dir)
{
    this->dir = dir;
}


AutoCloseDir::operator DIR *()
{
    return dir;
}



//////////////////////////////////////////////////////////////////////


Pid::Pid()
{
    pid = -1;
    separatePG = false;
}


Pid::~Pid()
{
    kill();
}


void Pid::operator =(pid_t pid)
{
    if (this->pid != pid) kill();
    this->pid = pid;
}


Pid::operator pid_t()
{
    return pid;
}


void Pid::kill()
{
    if (pid == -1) return;
    
    printMsg(lvlError, format("killing process %1%") % pid);

    /* Send a KILL signal to the child.  If it has its own process
       group, send the signal to every process in the child process
       group (which hopefully includes *all* its children). */
    if (::kill(separatePG ? -pid : pid, SIGKILL) != 0)
        printMsg(lvlError, (SysError(format("killing process %1%") % pid).msg()));

    /* Wait until the child dies, disregarding the exit status. */
    int status;
    while (waitpid(pid, &status, 0) == -1)
        if (errno != EINTR) printMsg(lvlError,
            (SysError(format("waiting for process %1%") % pid).msg()));

    pid = -1;
}


int Pid::wait(bool block)
{
    while (1) {
        int status;
        int res = waitpid(pid, &status, block ? 0 : WNOHANG);
        if (res == pid) {
            pid = -1;
            return status;
        }
        if (res == 0 && !block) return -1;
        if (errno != EINTR)
            throw SysError("cannot get child exit status");
    }
}


void Pid::setSeparatePG(bool separatePG)
{
    this->separatePG = separatePG;
}



//////////////////////////////////////////////////////////////////////


string runProgram(Path program)
{
    /* Create a pipe. */
    Pipe pipe;
    pipe.create();

    /* Fork. */
    Pid pid;
    pid = fork();
    switch (pid) {

    case -1:
        throw SysError("unable to fork");

    case 0: /* child */
        try {
            pipe.readSide.close();

            if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
                throw SysError("dupping from-hook write side");
            
            execl(program.c_str(), program.c_str(), (char *) 0);
            throw SysError(format("executing `%1%'") % program);
            
        } catch (std::exception & e) {
            std::cerr << "error: " << e.what() << std::endl;
        }
        quickExit(1);
    }

    /* Parent. */

    pipe.writeSide.close();

    string result = drainFD(pipe.readSide);

    /* Wait for the child to finish. */
    int status = pid.wait(true);
    if (!statusOk(status))
        throw Error(format("program `%1% %2%")
            % program % statusToString(status));

    return result;
}


void quickExit(int status)
{
#ifdef __CYGWIN__
    /* Hack for Cygwin: _exit() doesn't seem to work quite right,
       since some Berkeley DB code appears to be called when a child
       exits through _exit() (e.g., because execve() failed).  So call
       the Windows API directly. */
    ExitProcess(status);
#else
    _exit(status);
#endif
}


//////////////////////////////////////////////////////////////////////


volatile sig_atomic_t _isInterrupted = 0;

void _interrupted()
{
    /* Block user interrupts while an exception is being handled.
       Throwing an exception while another exception is being handled
       kills the program! */
    if (!std::uncaught_exception()) {
        _isInterrupted = 0;
        throw Error("interrupted by the user");
    }
}



//////////////////////////////////////////////////////////////////////


string packStrings(const Strings & strings)
{
    string d;
    for (Strings::const_iterator i = strings.begin();
         i != strings.end(); ++i)
    {
        unsigned int len = i->size();
        d += len & 0xff;
        d += (len >> 8) & 0xff;
        d += (len >> 16) & 0xff;
        d += (len >> 24) & 0xff;
        d += *i;
    }
    return d;
}

    
Strings unpackStrings(const string & s)
{
    Strings strings;
    
    string::const_iterator i = s.begin();
    
    while (i != s.end()) {

        if (i + 4 > s.end())
            throw Error(format("short db entry: `%1%'") % s);
        
        unsigned int len;
        len = (unsigned char) *i++;
        len |= ((unsigned char) *i++) << 8;
        len |= ((unsigned char) *i++) << 16;
        len |= ((unsigned char) *i++) << 24;

        if (len == 0xffffffff) return strings; /* explicit end-of-list */
        
        if (i + len > s.end())
            throw Error(format("short db entry: `%1%'") % s);

        strings.push_back(string(i, i + len));
        i += len;
    }
    
    return strings;
}


Strings tokenizeString(const string & s, const string & separators)
{
    Strings result;
    string::size_type pos = s.find_first_not_of(separators, 0);
    while (pos != string::npos) {
        string::size_type end = s.find_first_of(separators, pos + 1);
        if (end == string::npos) end = s.size();
        string token(s, pos, end - pos);
        result.push_back(token);
        pos = s.find_first_not_of(separators, end);
    }
    return result;
}


string statusToString(int status)
{
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        if (WIFEXITED(status))
            return (format("failed with exit code %1%") % WEXITSTATUS(status)).str();
        else if (WIFSIGNALED(status))
            return (format("failed due to signal %1%") % WTERMSIG(status)).str();
        else
            return "died abnormally";
    } else return "succeeded";
}


bool statusOk(int status)
{
    return WIFEXITED(status) && WEXITSTATUS(status) == 0;
}


string int2String(int n)
{
    std::ostringstream str;
    str << n;
    return str.str();
}


bool string2Int(const string & s, int & n)
{
    std::istringstream str(s);
    str >> n;
    return str && str.get() == EOF;
}

 
//////////////////////////////////////////////////////////////////////


static bool haveSwitched;
static uid_t savedUid, nixUid;
static gid_t savedGid, nixGid;


#if HAVE_SETRESUID
#define _setuid(uid) setresuid(uid, uid, savedUid)
#define _setgid(gid) setresgid(gid, gid, savedGid)
#else
/* Only works properly when run by root. */
#define _setuid(uid) setuid(uid)
#define _setgid(gid) setgid(gid)
#endif


SwitchToOriginalUser::SwitchToOriginalUser()
{
#if HAVE_SETRESUID
    /* Temporarily switch the effective uid/gid back to the saved
       uid/gid (which is the uid/gid of the user that executed the Nix
       program; it's *not* the real uid/gid, since we changed that to
       the Nix user in switchToNixUser()). */
    if (haveSwitched) {
        if (setuid(savedUid) == -1)
            throw SysError(format("temporarily restoring uid to `%1%'") % savedUid); 
        if (setgid(savedGid) == -1)
            throw SysError(format("temporarily restoring gid to `%1%'") % savedGid); 
    }
#endif
}


SwitchToOriginalUser::~SwitchToOriginalUser()
{
#if HAVE_SETRESUID
    /* Switch the effective uid/gid back to the Nix user. */
    if (haveSwitched) {
        if (setuid(nixUid) == -1)
            throw SysError(format("restoring uid to `%1%'") % nixUid); 
        if (setgid(nixGid) == -1)
            throw SysError(format("restoring gid to `%1%'") % nixGid); 
    }
#endif
}


void switchToNixUser()
{
    fprintf(stderr, "real = %d/%d, effective = %d/%d\n",
        getuid(), getgid(), geteuid(), getegid());

    /* Note: we require setresuid for now since I don't want to think
       to deeply about whether this works on systems that don't have
       setresuid.  It's already hard enough. */
      
#if HAVE_SETRESUID

    /* Setuid Nix operation works as follows:

       - The Nix binaries are owned by a Nix user and group, e.g.,
         nix.nix, and must setuid and setgid, e.g.,

         rwsrwsr-x nix.nix

       - Users (say alice.users) are only allowed to run (most) Nix
         operations if they are in the Nix group.  If they aren't,
         some read-only operations (like nix-env -qa) may still work.
         
       - We run mostly under the Nix user/group, but we switch back to
         the calling user/group for some work, like reading Nix
         expressions.

    */
    
    
    /* Don't do anything if this is not a setuid binary. */
    if (getuid() == geteuid() && getgid() == getegid()) return;

    /* 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.  (The Nix group is the group of the current executable,
       i.e., the current effective gid.)  Otherwise we just drop all
       privileges. */

    nixGid = geteuid();

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

    /* !!! Apparently it is unspecified whether getgroups() includes
       the effective gid.  In that case the following test is always
       true *if* the program is installed setgid (which we do when we
       have setresuid()).  On Linux this doesn't appear to be the
       case, but we should switch to the real gid before doing this
       test, and then switch back to the saved gid. */ 

    /* 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] == nixGid) {
            found = true;
            break;
        }

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

    /* Save the uid/gid of the caller so the we can switch back to
       that uid/gid for temporary work, like accessing files, in
       SwitchToOriginaluser. */
    savedUid = getuid();
    savedGid = getgid();

    /* Set the real and effective gids to nixGid.  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(nixGid) != 0 || getgid() != nixGid || getegid() != nixGid) {
        std::cerr << format("unable to set gid to `%1%'\n") % nixGid;
        exit(1);
    }

    /* The Nix uid is the effective uid of the owner of the current
       executable, i.e., the current effective uid. */
    nixUid = geteuid();

    /* 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(nixUid) != 0 || getuid() != nixUid || geteuid() != nixUid) {
        std::cerr << format("unable to set uid to `%1%'\n") % nixUid;
        exit(1);
    }

    /* !!! for setuid operation, we should: 1) wipe the environment;
       2) verify file descriptors 0, 1, 2; 3) etc.
       See: http://www.daemon-systems.org/man/setuid.7.html
    */

    haveSwitched = true;
#endif
}


}