Remove nix-setuid-helper

AFAIK, nobody uses it, it's not maintained, and it has no tests.

13 files changed, 50 insertions, 526 deletions

diff --git a/.gitignore b/.gitignore
index 8a7e99d0676b..5dc9af7fc018 100644
--- a/.gitignore
+++ b/.gitignore
@@ -100,9 +100,6 @@ Makefile.in
 /src/nix-log2xml/*.xml
 /src/nix-log2xml/*.html
 
-# /src/nix-setuid-helper/
-/src/nix-setuid-helper/nix-setuid-helper
-
 # /src/nix-store/
 /src/nix-store/nix-store
 
diff --git a/configure.ac b/configure.ac
index abf4136a90a2..7acd57557495 100644
--- a/configure.ac
+++ b/configure.ac
@@ -375,7 +375,6 @@ AC_CONFIG_FILES([Makefile
    src/nix-instantiate/Makefile
    src/nix-env/Makefile
    src/nix-daemon/Makefile
-   src/nix-setuid-helper/Makefile
    src/nix-log2xml/Makefile
    src/bsdiff-4.3/Makefile
    perl/Makefile
diff --git a/doc/manual/installation.xml b/doc/manual/installation.xml
index 9d1a7e755c53..a136d3b1129e 100644
--- a/doc/manual/installation.xml
+++ b/doc/manual/installation.xml
@@ -380,7 +380,7 @@ group should be the build users group, and it should have the sticky
 bit turned on (like <filename>/tmp</filename>):
 
 <screen>
-$ chgrp nixbld /nix/store
+$ chown root.nixbld /nix/store
 $ chmod 1775 /nix/store
 </screen>
 
@@ -401,15 +401,7 @@ build-users-group = nixbld
 </section>
 
 
-<section><title>Nix store/database owned by root</title>
-
-<para>The simplest setup is to let <literal>root</literal> own the Nix
-store and database.  I.e.,
-
-<screen>
-$ chown -R root /nix/store /nix/var/nix</screen>
-
-</para>
+<section><title>Running the daemon</title>
 
 <para>The <link linkend="sec-nix-daemon">Nix daemon</link> should be
 started as follows (as <literal>root</literal>):
@@ -433,72 +425,6 @@ into the users’ login scripts.</para>
 </section>
 
 
-<section><title>Nix store/database not owned by root</title>
-
-<para>It is also possible to let the Nix store and database be owned
-by a non-root user, which should be more secure<footnote><para>Note
-however that even when the Nix daemon runs as root, not
-<emphasis>that</emphasis> much code is executed as root: Nix
-expression evaluation is performed by the calling (unprivileged) user,
-and builds are performed under the special build user accounts.  So
-only the code that accesses the database and starts builds is executed
-as <literal>root</literal>.</para></footnote>.  Typically, this user
-is a special account called <literal>nix</literal>, but it can be
-named anything.  It should own the Nix store and database:
-
-<screen>
-$ chown -R nix /nix/store /nix/var/nix</screen>
-
-and of course <command>nix-daemon</command> should be started under
-that user, e.g.,
-
-<screen>
-$ su - nix -c "exec /nix/bin/nix-daemon"</screen>
-
-</para>
-
-<para>There is a catch, though: non-<literal>root</literal> users
-cannot start builds under the build user accounts, since the
-<function>setuid</function> system call is obviously privileged.  To
-allow a non-<literal>root</literal> Nix daemon to use the build user
-feature, it calls a setuid-root helper program,
-<command>nix-setuid-helper</command>.  This program is installed in
-<filename><replaceable>prefix</replaceable>/libexec/nix-setuid-helper</filename>.
-To set the permissions properly (Nix’s <command>make install</command>
-doesn’t do this, since we don’t want to ship setuid-root programs
-out-of-the-box):
-
-<screen>
-$ chown root.root /nix/libexec/nix-setuid-helper
-$ chmod 4755 /nix/libexec/nix-setuid-helper
-</screen>
-
-(This example assumes that the Nix binaries are installed in
-<filename>/nix</filename>.)</para>
-
-<para>Of course, the <command>nix-setuid-helper</command> command
-should not be usable by just anybody, since then anybody could run
-commands under the Nix build user accounts.  For that reason there is
-a configuration file <filename>/etc/nix-setuid.conf</filename> that
-restricts the use of the helper.  This file should be a text file
-containing precisely two lines, the first being the Nix daemon user
-and the second being the build users group, e.g.,
-
-<programlisting>
-nix
-nixbld
-</programlisting>
-
-The setuid-helper barfs if it is called by a user other than the one
-specified on the first line, or if it is asked to execute a build
-under a user who is not a member of the group specified on the second
-line.  The file <filename>/etc/nix-setuid.conf</filename> must be
-owned by root, and must not be group- or world-writable.  The
-setuid-helper barfs if this is not the case.</para>
-
-</section>
-
-
 <section><title>Restricting access</title>
 
 <para>To limit which users can perform Nix operations, you can use the
diff --git a/doc/manual/release-notes.xml b/doc/manual/release-notes.xml
index 5d057881dbc0..3db083870405 100644
--- a/doc/manual/release-notes.xml
+++ b/doc/manual/release-notes.xml
@@ -7,6 +7,22 @@
 
 <!--==================================================================-->
 
+<section xml:id="ssec-relnotes-1.7"><title>Release 1.7 (TBA)</title>
+
+<para>This release has the following changes:</para>
+
+<itemizedlist>
+
+  <listitem><para><command>nix-setuid-helper</command> is
+  gone.</para></listitem>
+
+</itemizedlist>
+
+</section>
+
+
+<!--==================================================================-->
+
 <section xml:id="ssec-relnotes-1.6.1"><title>Release 1.6.1 (October 28, 2013)</title>
 
 <para>This is primarily a bug fix release.  Changes of interest
diff --git a/src/Makefile.am b/src/Makefile.am
index 0ae407c573d1..a5e411b9ed6e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,3 +1,3 @@
 SUBDIRS = boost libutil libstore libmain nix-store nix-hash \
- libexpr nix-instantiate nix-env nix-daemon nix-setuid-helper \
+ libexpr nix-instantiate nix-env nix-daemon \
  nix-log2xml bsdiff-4.3
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 51314f7368f0..63e34d256057 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -549,93 +549,10 @@ void UserLock::release()
 }
 
 
-static void runSetuidHelper(const string & command,
-    const string & arg)
-{
-    Path program = getEnv("NIX_SETUID_HELPER",
-        settings.nixLibexecDir + "/nix-setuid-helper");
-
-    /* Fork. */
-    Pid pid;
-    pid = fork();
-    switch (pid) {
-
-    case -1:
-        throw SysError("unable to fork");
-
-    case 0: /* child */
-        try {
-            std::vector<const char *> args; /* careful with c_str()! */
-            args.push_back(program.c_str());
-            args.push_back(command.c_str());
-            args.push_back(arg.c_str());
-            args.push_back(0);
-
-            restoreSIGPIPE();
-            restoreAffinity();
-
-            execve(program.c_str(), (char * *) &args[0], 0);
-            throw SysError(format("executing `%1%'") % program);
-        }
-        catch (std::exception & e) {
-            writeToStderr("error: " + string(e.what()) + "\n");
-        }
-        _exit(1);
-    }
-
-    /* Parent. */
-
-    /* Wait for the child to finish. */
-    int status = pid.wait(true);
-    if (!statusOk(status))
-        throw Error(format("program `%1%' %2%")
-            % program % statusToString(status));
-}
-
-
 void UserLock::kill()
 {
     assert(enabled());
-    if (amPrivileged())
-        killUser(uid);
-    else
-        runSetuidHelper("kill", user);
-}
-
-
-bool amPrivileged()
-{
-    return geteuid() == 0;
-}
-
-
-void getOwnership(const Path & path)
-{
-    runSetuidHelper("get-ownership", path);
-}
-
-
-void deletePathWrapped(const Path & path, unsigned long long & bytesFreed)
-{
-    try {
-        /* First try to delete it ourselves. */
-        deletePath(path, bytesFreed);
-    } catch (SysError & e) {
-        /* If this failed due to a permission error, then try it with
-           the setuid helper. */
-        if (settings.buildUsersGroup != "" && !amPrivileged()) {
-            getOwnership(path);
-            deletePath(path, bytesFreed);
-        } else
-            throw;
-    }
-}
-
-
-void deletePathWrapped(const Path & path)
-{
-    unsigned long long dummy1;
-    deletePathWrapped(path, dummy1);
+    killUser(uid);
 }
 
 
@@ -971,15 +888,11 @@ void DerivationGoal::killChild()
         worker.childTerminated(pid);
 
         if (buildUser.enabled()) {
-            /* We can't use pid.kill(), since we may not have the
-               appropriate privilege.  I.e., if we're not root, then
-               setuid helper should do it).
-
-               Also, if we're using a build user, then there is a
-               tricky race condition: if we kill the build user before
-               the child has done its setuid() to the build user uid,
-               then it won't be killed, and we'll potentially lock up
-               in pid.wait().  So also send a conventional kill to the
+            /* If we're using a build user, then there is a tricky
+               race condition: if we kill the build user before the
+               child has done its setuid() to the build user uid, then
+               it won't be killed, and we'll potentially lock up in
+               pid.wait().  So also send a conventional kill to the
                child. */
             ::kill(-pid, SIGKILL); /* ignore the result */
             buildUser.kill();
@@ -1349,7 +1262,7 @@ void DerivationGoal::tryToBuild()
         if (worker.store.isValidPath(path)) continue;
         if (!pathExists(path)) continue;
         debug(format("removing unregistered path `%1%'") % path);
-        deletePathWrapped(path);
+        deletePath(path);
     }
 
     /* Check again whether any output previously failed to build,
@@ -1427,7 +1340,7 @@ void replaceValidPath(const Path & storePath, const Path tmpPath)
     if (rename(tmpPath.c_str(), storePath.c_str()) == -1)
         throw SysError(format("moving `%1%' to `%2%'") % tmpPath % storePath);
     if (pathExists(oldPath))
-        deletePathWrapped(oldPath);
+        deletePath(oldPath);
 }
 
 
@@ -1532,13 +1445,6 @@ void DerivationGoal::buildDone()
 
                 rewrittenPaths.insert(path);
             }
-
-            /* Gain ownership of the build result using the setuid
-               wrapper if we're not root.  If we *are* root, then
-               canonicalisePathMetaData() will take care of this later
-               on. */
-            if (buildUser.enabled() && !amPrivileged())
-                getOwnership(path);
         }
 
         /* Check the exit status. */
@@ -1846,13 +1752,9 @@ void DerivationGoal::startBuilder()
            uid. */
         buildUser.kill();
 
-        /* Change ownership of the temporary build directory, if we're
-           root.  If we're not root, then the setuid helper will do it
-           just before it starts the builder. */
-        if (amPrivileged()) {
-            if (chown(tmpDir.c_str(), buildUser.getUID(), buildUser.getGID()) == -1)
-                throw SysError(format("cannot change ownership of `%1%'") % tmpDir);
-        }
+        /* Change ownership of the temporary build directory. */
+        if (chown(tmpDir.c_str(), buildUser.getUID(), buildUser.getGID()) == -1)
+            throw SysError(format("cannot change ownership of `%1%'") % tmpDir);
 
         /* Check that the Nix store has the appropriate permissions,
            i.e., owned by root and mode 1775 (sticky bit on so that
@@ -2212,30 +2114,18 @@ void DerivationGoal::initChild()
         if (buildUser.enabled()) {
             printMsg(lvlChatty, format("switching to user `%1%'") % buildUser.getUser());
 
-            if (amPrivileged()) {
-
-                if (setgroups(0, 0) == -1)
-                    throw SysError("cannot clear the set of supplementary groups");
-
-                if (setgid(buildUser.getGID()) == -1 ||
-                    getgid() != buildUser.getGID() ||
-                    getegid() != buildUser.getGID())
-                    throw SysError("setgid failed");
-
-                if (setuid(buildUser.getUID()) == -1 ||
-                    getuid() != buildUser.getUID() ||
-                    geteuid() != buildUser.getUID())
-                    throw SysError("setuid failed");
-
-            } else {
-                /* Let the setuid helper take care of it. */
-                program = settings.nixLibexecDir + "/nix-setuid-helper";
-                args.push_back(program.c_str());
-                args.push_back("run-builder");
-                user = buildUser.getUser().c_str();
-                args.push_back(user.c_str());
-                args.push_back(drv.builder.c_str());
-            }
+            if (setgroups(0, 0) == -1)
+                throw SysError("cannot clear the set of supplementary groups");
+
+            if (setgid(buildUser.getGID()) == -1 ||
+                getgid() != buildUser.getGID() ||
+                getegid() != buildUser.getGID())
+                throw SysError("setgid failed");
+
+            if (setuid(buildUser.getUID()) == -1 ||
+                getuid() != buildUser.getUID() ||
+                geteuid() != buildUser.getUID())
+                throw SysError("setuid failed");
         }
 
         /* Fill in the arguments. */
@@ -2466,12 +2356,10 @@ void DerivationGoal::deleteTmpDir(bool force)
             printMsg(lvlError,
                 format("note: keeping build directory `%2%'")
                 % drvPath % tmpDir);
-            if (buildUser.enabled() && !amPrivileged())
-                getOwnership(tmpDir);
             chmod(tmpDir.c_str(), 0755);
         }
         else
-            deletePathWrapped(tmpDir);
+            deletePath(tmpDir);
         tmpDir = "";
     }
 }
@@ -2548,7 +2436,7 @@ Path DerivationGoal::addHashRewrite(const Path & path)
     string h1 = string(path, settings.nixStore.size() + 1, 32);
     string h2 = string(printHash32(hashString(htSHA256, "rewrite:" + drvPath + ":" + path)), 0, 32);
     Path p = settings.nixStore + "/" + h2 + string(path, settings.nixStore.size() + 33);
-    if (pathExists(p)) deletePathWrapped(p);
+    if (pathExists(p)) deletePath(p);
     assert(path.size() == p.size());
     rewritesToTmp[h1] = h2;
     rewritesFromTmp[h2] = h1;
@@ -2639,9 +2527,6 @@ SubstitutionGoal::SubstitutionGoal(const Path & storePath, Worker & worker, bool
 
 SubstitutionGoal::~SubstitutionGoal()
 {
-    /* !!! Once we let substitution goals run under a build user, we
-       need to use the setuid helper just as in ~DerivationGoal().
-       Idem for cancel. */
     if (pid != -1) worker.childTerminated(pid);
 }
 
@@ -2792,7 +2677,7 @@ void SubstitutionGoal::tryToRun()
 
     /* Remove the (stale) output path if it exists. */
     if (pathExists(destPath))
-        deletePathWrapped(destPath);
+        deletePath(destPath);
 
     worker.store.setSubstituterEnv();
 
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index f32329960c66..ce9b10f0538b 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -415,7 +415,7 @@ bool LocalStore::isActiveTempFile(const GCState & state,
 void LocalStore::deleteGarbage(GCState & state, const Path & path)
 {
     unsigned long long bytesFreed;
-    deletePathWrapped(path, bytesFreed);
+    deletePath(path, bytesFreed);
     state.results.bytesFreed += bytesFreed;
 }
 
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 24d6acc2f403..8aa113796da1 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1328,7 +1328,7 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
 
         if (repair || !isValidPath(dstPath)) {
 
-            if (pathExists(dstPath)) deletePathWrapped(dstPath);
+            if (pathExists(dstPath)) deletePath(dstPath);
 
             if (recursive) {
                 StringSource source(dump);
@@ -1397,7 +1397,7 @@ Path LocalStore::addTextToStore(const string & name, const string & s,
 
         if (repair || !isValidPath(dstPath)) {
 
-            if (pathExists(dstPath)) deletePathWrapped(dstPath);
+            if (pathExists(dstPath)) deletePath(dstPath);
 
             writeFile(dstPath, s);
 
@@ -1630,7 +1630,7 @@ Path LocalStore::importPath(bool requireSignature, Source & source)
 
         if (!isValidPath(dstPath)) {
 
-            if (pathExists(dstPath)) deletePathWrapped(dstPath);
+            if (pathExists(dstPath)) deletePath(dstPath);
 
             if (rename(unpacked.c_str(), dstPath.c_str()) == -1)
                 throw SysError(format("cannot move `%1%' to `%2%'")
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
index adba52fd46a9..1ace7cec996b 100644
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -322,7 +322,7 @@ typedef set<Inode> InodesSeen;
    - the permissions are set of 444 or 555 (i.e., read-only with or
      without execute permission; setuid bits etc. are cleared)
    - the owner and group are set to the Nix user and group, if we're
-     in a setuid Nix installation. */
+     running as root. */
 void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & inodesSeen);
 void canonicalisePathMetaData(const Path & path, uid_t fromUid);
 
@@ -330,16 +330,4 @@ void canonicaliseTimestampAndPermissions(const Path & path);
 
 MakeError(PathInUse, Error);
 
-/* Whether we are root. */
-bool amPrivileged();
-
-/* Recursively change the ownership of `path' to the current uid. */
-void getOwnership(const Path & path);
-
-/* Like deletePath(), but changes the ownership of `path' using the
-   setuid wrapper if necessary (and possible). */
-void deletePathWrapped(const Path & path, unsigned long long & bytesFreed);
-
-void deletePathWrapped(const Path & path);
-
 }
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 8fd61826fa28..9437a2f99a3c 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -968,19 +968,6 @@ void closeOnExec(int fd)
 }
 
 
-void setuidCleanup()
-{
-    /* Don't trust the environment. */
-    environ = 0;
-
-    /* Make sure that file descriptors 0, 1, 2 are open. */
-    for (int fd = 0; fd <= 2; ++fd) {
-        struct stat st;
-        if (fstat(fd, &st) == -1) abort();
-    }
-}
-
-
 #if HAVE_VFORK
 pid_t (*maybeVfork)() = vfork;
 #else
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 86c65b763d00..2335cbf98820 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -268,10 +268,6 @@ void closeMostFDs(const set<int> & exceptions);
 /* Set the close-on-exec flag for the given file descriptor. */
 void closeOnExec(int fd);
 
-/* Common initialisation for setuid programs: clear the environment,
-   sanitize file handles 0, 1 and 2. */
-void setuidCleanup();
-
 /* Call vfork() if available, otherwise fork(). */
 extern pid_t (*maybeVfork)();
 
diff --git a/src/nix-setuid-helper/Makefile.am b/src/nix-setuid-helper/Makefile.am
deleted file mode 100644
index a04701636d84..000000000000
--- a/src/nix-setuid-helper/Makefile.am
+++ /dev/null
@@ -1,7 +0,0 @@
-libexec_PROGRAMS = nix-setuid-helper
-
-nix_setuid_helper_SOURCES = nix-setuid-helper.cc
-nix_setuid_helper_LDADD = ../libutil/libutil.la \
- ../boost/format/libformat.la
-
-AM_CXXFLAGS = -I$(srcdir)/.. -I$(srcdir)/../libutil
diff --git a/src/nix-setuid-helper/nix-setuid-helper.cc b/src/nix-setuid-helper/nix-setuid-helper.cc
deleted file mode 100644
index 697964088c2a..000000000000
--- a/src/nix-setuid-helper/nix-setuid-helper.cc
+++ /dev/null
@@ -1,263 +0,0 @@
-#include "config.h"
-
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <unistd.h>
-#include <fcntl.h>
-#include <stdlib.h>
-
-#include <pwd.h>
-#include <grp.h>
-
-#include <iostream>
-#include <vector>
-
-#include "util.hh"
-
-using namespace nix;
-
-
-extern char * * environ;
-
-
-/* Recursively change the ownership of `path' to user `uidTo' and
-   group `gidTo'.  `path' must currently be owned by user `uidFrom',
-   or, if `uidFrom' is -1, by group `gidFrom'. */
-static void secureChown(uid_t uidFrom, gid_t gidFrom,
-    uid_t uidTo, gid_t gidTo, const Path & path)
-{
-    format error = format("cannot change ownership of `%1%'") % path;
-    
-    struct stat st;
-    if (lstat(path.c_str(), &st) == -1)
-        /* Important: don't give any detailed error messages here.
-           Otherwise, the Nix account can discover information about
-           the existence of paths that it doesn't normally have access
-           to. */
-        throw Error(error);
-
-    if (uidFrom != (uid_t) -1) {
-        assert(uidFrom != 0);
-        if (st.st_uid != uidFrom)
-            throw Error(error);
-    } else {
-        assert(gidFrom != 0);
-        if (st.st_gid != gidFrom)
-            throw Error(error);
-    }
-
-    assert(uidTo != 0 && gidTo != 0);
-
-#if HAVE_LCHOWN
-    if (lchown(path.c_str(), uidTo, gidTo) == -1)
-        throw Error(error);
-#else
-    if (!S_ISLNK(st.st_mode) &&
-        chown(path.c_str(), uidTo, gidTo) == -1)
-        throw Error(error);
-#endif
-
-    if (S_ISDIR(st.st_mode)) {
-        Strings names = readDirectory(path);
-	for (Strings::iterator i = names.begin(); i != names.end(); ++i)
-            /* !!! recursion; check stack depth */
-	    secureChown(uidFrom, gidFrom, uidTo, gidTo, path + "/" + *i);
-    }
-}
-
-
-static uid_t nameToUid(const string & userName)
-{
-    struct passwd * pw = getpwnam(userName.c_str());
-    if (!pw)
-        throw Error(format("user `%1%' does not exist") % userName);
-    return pw->pw_uid;
-}
-
-
-static void checkIfBuildUser(const StringSet & buildUsers,
-    const string & userName)
-{
-    if (buildUsers.find(userName) == buildUsers.end())
-        throw Error(format("user `%1%' is not a member of the build users group")
-            % userName);
-}
-
-
-/* Run `program' under user account `targetUser'.  `targetUser' should
-   be a member of `buildUsersGroup'.  The ownership of the current
-   directory is changed from the Nix user (uidNix) to the target
-   user. */
-static void runBuilder(uid_t uidNix, gid_t gidBuildUsers,
-    const StringSet & buildUsers, const string & targetUser,
-    string program, int argc, char * * argv, char * * env)
-{
-    uid_t uidTargetUser = nameToUid(targetUser);
-
-    /* Sanity check. */
-    if (uidTargetUser == 0)
-        throw Error("won't setuid to root");
-
-    /* Verify that the target user is a member of the build users
-       group. */
-    checkIfBuildUser(buildUsers, targetUser);
-    
-    /* Chown the current directory, *if* it is owned by the Nix
-       account.  The idea is that the current directory is the
-       temporary build directory in /tmp or somewhere else, and we
-       don't want to create that directory here. */
-    secureChown(uidNix, (gid_t) -1, uidTargetUser, gidBuildUsers, ".");
-
-    /* Set the real, effective and saved gid.  Must be done before
-       setuid(), otherwise it won't set the real and saved gids. */
-    if (setgroups(0, 0) == -1)
-        throw SysError("cannot clear the set of supplementary groups");
-
-    if (setgid(gidBuildUsers) == -1 ||
-        getgid() != gidBuildUsers ||
-        getegid() != gidBuildUsers)
-        throw SysError("setgid failed");
-
-    /* Set the real, effective and saved uid. */
-    if (setuid(uidTargetUser) == -1 ||
-        getuid() != uidTargetUser ||
-        geteuid() != uidTargetUser)
-        throw SysError("setuid failed");
-
-    /* Execute the program. */
-    std::vector<const char *> args;
-    for (int i = 0; i < argc; ++i)
-        args.push_back(argv[i]);
-    args.push_back(0);
-
-    environ = env;
-
-    /* Glibc clears TMPDIR in setuid programs (see
-       sysdeps/generic/unsecvars.h in the Glibc sources), so bring it
-       back. */
-    setenv("TMPDIR", getenv("NIX_BUILD_TOP"), 1);
-    
-    if (execv(program.c_str(), (char * *) &args[0]) == -1)
-        throw SysError(format("cannot execute `%1%'") % program);
-}
-
-
-void killBuildUser(gid_t gidBuildUsers,
-    const StringSet & buildUsers, const string & userName)
-{
-    uid_t uid = nameToUid(userName);
-    
-    /* Verify that the user whose processes we are to kill is a member
-       of the build users group. */
-    checkIfBuildUser(buildUsers, userName);
-
-    assert(uid != 0);
-
-    killUser(uid);
-}
-
-
-#ifndef NIX_SETUID_CONFIG_FILE
-#define NIX_SETUID_CONFIG_FILE "/etc/nix-setuid.conf"
-#endif
-
-
-static void run(int argc, char * * argv) 
-{
-    char * * oldEnviron = environ;
-    
-    setuidCleanup();
-
-    if (geteuid() != 0)
-        throw Error("nix-setuid-wrapper must be setuid root");
-
-
-    /* Read the configuration file.  It should consist of two words:
-       
-       <nix-user-name> <nix-builders-group>
-
-       The first is the privileged account under which the main Nix
-       processes run (i.e., the supposed caller).  It should match our
-       real uid.  The second is the Unix group to which the Nix
-       builders belong (and nothing else!). */
-    string configFile = NIX_SETUID_CONFIG_FILE;
-    AutoCloseFD fdConfig = open(configFile.c_str(), O_RDONLY);
-    if (fdConfig == -1)
-        throw SysError(format("opening `%1%'") % configFile);
-
-    /* Config file should be owned by root. */
-    struct stat st;
-    if (fstat(fdConfig, &st) == -1) throw SysError("statting file");
-    if (st.st_uid != 0)
-        throw Error(format("`%1%' not owned by root") % configFile);
-    if (st.st_mode & (S_IWGRP | S_IWOTH))
-        throw Error(format("`%1%' should not be group or world-writable") % configFile);
-
-    vector<string> tokens = tokenizeString<vector<string> >(readFile(fdConfig));
-
-    fdConfig.close();
-
-    if (tokens.size() != 2)
-        throw Error(format("parse error in `%1%'") % configFile);
-
-    string nixUser = tokens[0];
-    string buildUsersGroup = tokens[1];
-
-
-    /* Check that the caller (real uid) is the one allowed to call
-       this program. */
-    uid_t uidNix = nameToUid(nixUser);
-    if (uidNix != getuid())
-        throw Error("you are not allowed to call this program, go away");
-    
-    
-    /* Get the gid and members of buildUsersGroup. */
-    struct group * gr = getgrnam(buildUsersGroup.c_str());
-    if (!gr)
-        throw Error(format("group `%1%' does not exist") % buildUsersGroup);
-    gid_t gidBuildUsers = gr->gr_gid;
-
-    StringSet buildUsers;
-    for (char * * p = gr->gr_mem; *p; ++p)
-        buildUsers.insert(*p);
-
-    
-    /* Perform the desired command. */
-    if (argc < 2)
-        throw Error("invalid arguments");
-
-    string command(argv[1]);
-
-    if (command == "run-builder") {
-        /* Syntax: nix-setuid-helper run-builder <username> <program>
-             <arg0 arg1...> */
-        if (argc < 4) throw Error("missing user name / program name");
-        runBuilder(uidNix, gidBuildUsers, buildUsers,
-            argv[2], argv[3], argc - 4, argv + 4, oldEnviron);
-    }
-
-    else if (command == "get-ownership") {
-        /* Syntax: nix-setuid-helper get-ownership <path> */
-        if (argc != 3) throw Error("missing path");
-        secureChown((uid_t) -1, gidBuildUsers, uidNix, gidBuildUsers, argv[2]);
-    }
-
-    else if (command == "kill") {
-        /* Syntax: nix-setuid-helper kill <username> */
-        if (argc != 3) throw Error("missing user name");
-        killBuildUser(gidBuildUsers, buildUsers, argv[2]);
-    }
-
-    else throw Error ("invalid command");
-}
-
-
-int main(int argc, char * * argv)
-{
-    try {
-        run(argc, argv);
-    } catch (Error & e) {
-        std::cerr << e.msg() << std::endl;
-        return 1;
-    }
-}