* Remove most of the old setuid code.

* Much simpler setuid code for the worker in slave mode.

src/libmain/shared.cc

@@ -15,6 +15,9 @@
 #include <aterm2.h>
 
 
+extern char * * environ;
+
+
 namespace nix {
 
 
@@ -204,6 +207,54 @@ static void initAndRun(int argc, char * * argv)
 }
 
 
+static void setuidInit()
+{
+    /* Don't do anything if this is not a setuid binary. */
+    if (getuid() == geteuid() && getgid() == getegid()) return;
+
+    uid_t nixUid = geteuid();
+    gid_t nixGid = getegid();
+    
+    fprintf(stderr, "<<< setuid mode >>>\n");
+
+    /* Don't trust the environment. */
+    environ = 0;
+
+    /* Don't trust the current directory. */
+    if (chdir("/") == -1) abort();
+
+    /* 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();
+    }
+
+    /* Set the real (and preferably also the save) uid/gid to the
+       effective uid/gid.  This matters mostly when we're not using
+       build-users (bad!), since some builders (like Perl) complain
+       when real != effective.
+
+       On systems where setresuid is unavailable, we can't drop the
+       saved uid/gid.  This means that we could go back to the
+       original real uid (i.e., the uid of the caller).  That's not
+       really a problem, except maybe when we execute a builder and
+       we're not using build-users.  In that case, the builder may be
+       able to switch to the uid of the caller and possibly do bad
+       stuff.  But note that when not using build-users, the builder
+       could also modify the Nix executables (say, replace them by a
+       Trojan horse), so the problem is already there. */
+
+#if HAVE_SETRESUID
+    setresuid(nixUid, nixUid, nixUid);
+    setresgid(nixGid, nixGid, nixGid);
+#else
+    /* Note: doesn't set saved uid/gid! */
+    setuid(nixUid);
+    setgid(nixGid);
+#endif
+}
+
+
 }
 
 
@@ -212,10 +263,11 @@ static char buf[1024];
 int main(int argc, char * * argv)
 {
     using namespace nix;
-    
+
-    /* If we are setuid root, we have to get rid of the excess
+    /* If we're setuid, then we need to take some security precautions
-       privileges ASAP. */
+       right away. */
-    switchToNixUser();
+    if (argc == 0) abort();
+    setuidInit();
     
     /* ATerm setup. */
     ATerm bottomOfStack;

src/libutil/util.cc

@@ -11,11 +11,8 @@
 
 #include <sys/stat.h>
 #include <sys/wait.h>
-#include <fcntl.h>
-
 #include <sys/types.h>
-#include <pwd.h>
+#include <fcntl.h>
-#include <grp.h>
 
 #include "util.hh"
 
@@ -891,130 +888,4 @@ bool string2Int(const string & s, int & n)
 }
 
  
-//////////////////////////////////////////////////////////////////////
-
-
-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
-
-
-void switchToNixUser()
-{
-#if 0
-    fprintf(stderr, "real = %d/%d, effective = %d/%d\n",
-        getuid(), getgid(), geteuid(), getegid());
-#endif
-
-    /* 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
-}
-
-
 }

src/libutil/util.hh

@@ -249,10 +249,6 @@ string int2String(int n);
 bool string2Int(const string & s, int & n);
 
 
-/* Setuid support. */
-void switchToNixUser();
-
- 
 }