* Remove most of the old setuid code.
* Much simpler setuid code for the worker in slave mode.
This commit is contained in:
Eelco Dolstra
parent
9c9cdb06d0
commit
536595b072
3 changed files with 57 additions and 138 deletions
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@ -15,6 +15,9 @@
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#include <aterm2.h>
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extern char * * environ;
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namespace nix {
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@ -204,6 +207,54 @@ static void initAndRun(int argc, char * * argv)
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}
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static void setuidInit()
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{
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/* Don't do anything if this is not a setuid binary. */
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if (getuid() == geteuid() && getgid() == getegid()) return;
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uid_t nixUid = geteuid();
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gid_t nixGid = getegid();
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fprintf(stderr, "<<< setuid mode >>>\n");
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/* Don't trust the environment. */
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environ = 0;
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/* Don't trust the current directory. */
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if (chdir("/") == -1) abort();
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/* Make sure that file descriptors 0, 1, 2 are open. */
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for (int fd = 0; fd <= 2; ++fd) {
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struct stat st;
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if (fstat(fd, &st) == -1) abort();
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}
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/* Set the real (and preferably also the save) uid/gid to the
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effective uid/gid. This matters mostly when we're not using
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build-users (bad!), since some builders (like Perl) complain
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when real != effective.
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On systems where setresuid is unavailable, we can't drop the
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saved uid/gid. This means that we could go back to the
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original real uid (i.e., the uid of the caller). That's not
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really a problem, except maybe when we execute a builder and
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we're not using build-users. In that case, the builder may be
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able to switch to the uid of the caller and possibly do bad
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stuff. But note that when not using build-users, the builder
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could also modify the Nix executables (say, replace them by a
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Trojan horse), so the problem is already there. */
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#if HAVE_SETRESUID
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setresuid(nixUid, nixUid, nixUid);
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setresgid(nixGid, nixGid, nixGid);
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#else
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/* Note: doesn't set saved uid/gid! */
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setuid(nixUid);
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setgid(nixGid);
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#endif
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}
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}
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@ -212,10 +263,11 @@ static char buf[1024];
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int main(int argc, char * * argv)
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{
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using namespace nix;
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/* If we are setuid root, we have to get rid of the excess
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privileges ASAP. */
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switchToNixUser();
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/* If we're setuid, then we need to take some security precautions
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right away. */
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if (argc == 0) abort();
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setuidInit();
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/* ATerm setup. */
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ATerm bottomOfStack;
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@ -11,11 +11,8 @@
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#include <sys/stat.h>
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#include <sys/wait.h>
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#include <fcntl.h>
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#include <sys/types.h>
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#include <pwd.h>
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#include <grp.h>
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#include <fcntl.h>
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#include "util.hh"
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@ -891,130 +888,4 @@ bool string2Int(const string & s, int & n)
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}
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//////////////////////////////////////////////////////////////////////
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static bool haveSwitched;
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static uid_t savedUid, nixUid;
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static gid_t savedGid, nixGid;
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#if HAVE_SETRESUID
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#define _setuid(uid) setresuid(uid, uid, savedUid)
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#define _setgid(gid) setresgid(gid, gid, savedGid)
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#else
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/* Only works properly when run by root. */
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#define _setuid(uid) setuid(uid)
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#define _setgid(gid) setgid(gid)
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#endif
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void switchToNixUser()
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{
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#if 0
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fprintf(stderr, "real = %d/%d, effective = %d/%d\n",
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getuid(), getgid(), geteuid(), getegid());
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#endif
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/* Note: we require setresuid for now since I don't want to think
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to deeply about whether this works on systems that don't have
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setresuid. It's already hard enough. */
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#if HAVE_SETRESUID
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/* Setuid Nix operation works as follows:
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- The Nix binaries are owned by a Nix user and group, e.g.,
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nix.nix, and must setuid and setgid, e.g.,
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rwsrwsr-x nix.nix
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- Users (say alice.users) are only allowed to run (most) Nix
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operations if they are in the Nix group. If they aren't,
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some read-only operations (like nix-env -qa) may still work.
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- We run mostly under the Nix user/group, but we switch back to
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the calling user/group for some work, like reading Nix
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expressions.
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*/
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/* Don't do anything if this is not a setuid binary. */
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if (getuid() == geteuid() && getgid() == getegid()) return;
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/* Here we set the uid and gid to the Nix user and group,
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respectively, IF the current (real) user is a member of the Nix
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group. (The Nix group is the group of the current executable,
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i.e., the current effective gid.) Otherwise we just drop all
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privileges. */
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nixGid = geteuid();
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/* Get the supplementary group IDs for the current user. */
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int maxGids = 512, nrGids;
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gid_t gids[maxGids];
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if ((nrGids = getgroups(maxGids, gids)) == -1) {
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std::cerr << format("unable to query gids\n");
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exit(1);
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}
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/* !!! Apparently it is unspecified whether getgroups() includes
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the effective gid. In that case the following test is always
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true *if* the program is installed setgid (which we do when we
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have setresuid()). On Linux this doesn't appear to be the
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case, but we should switch to the real gid before doing this
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test, and then switch back to the saved gid. */
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/* Check that the current user is a member of the Nix group. */
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bool found = false;
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for (int i = 0; i < nrGids; ++i)
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if (gids[i] == nixGid) {
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found = true;
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break;
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}
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if (!found) {
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/* Not in the Nix group - drop all root/Nix privileges. */
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_setgid(getgid());
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_setuid(getuid());
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return;
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}
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/* Save the uid/gid of the caller so the we can switch back to
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that uid/gid for temporary work, like accessing files, in
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SwitchToOriginaluser. */
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savedUid = getuid();
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savedGid = getgid();
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/* Set the real and effective gids to nixGid. Also make very sure
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that this succeeded. We switch the gid first because we cannot
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do it after we have dropped root uid. */
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if (_setgid(nixGid) != 0 || getgid() != nixGid || getegid() != nixGid) {
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std::cerr << format("unable to set gid to `%1%'\n") % nixGid;
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exit(1);
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}
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/* The Nix uid is the effective uid of the owner of the current
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executable, i.e., the current effective uid. */
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nixUid = geteuid();
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/* This will drop all root privileges, setting the real, effective
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and saved uids to pw->pw_uid. Also make very sure that this
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succeeded.*/
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if (_setuid(nixUid) != 0 || getuid() != nixUid || geteuid() != nixUid) {
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std::cerr << format("unable to set uid to `%1%'\n") % nixUid;
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exit(1);
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}
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/* !!! for setuid operation, we should: 1) wipe the environment;
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2) verify file descriptors 0, 1, 2; 3) etc.
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See: http://www.daemon-systems.org/man/setuid.7.html
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*/
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haveSwitched = true;
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#endif
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}
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}
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@ -249,10 +249,6 @@ string int2String(int n);
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bool string2Int(const string & s, int & n);
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/* Setuid support. */
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void switchToNixUser();
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}
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