+ /*}}}*/
+bool DropPrivileges() /*{{{*/
+{
+ if(_config->FindB("Debug::NoDropPrivs", false) == true)
+ return true;
+
+#if __gnu_linux__
+#if defined(PR_SET_NO_NEW_PRIVS) && ( PR_SET_NO_NEW_PRIVS != 38 )
+#error "PR_SET_NO_NEW_PRIVS is defined, but with a different value than expected!"
+#endif
+ // see prctl(2), needs linux3.5 at runtime - magic constant to avoid it at buildtime
+ int ret = prctl(38, 1, 0, 0, 0);
+ // ignore EINVAL - kernel is too old to understand the option
+ if(ret < 0 && errno != EINVAL)
+ _error->Warning("PR_SET_NO_NEW_PRIVS failed with %i", ret);
+#endif
+
+ // empty setting disables privilege dropping - this also ensures
+ // backward compatibility, see bug #764506
+ const std::string toUser = _config->Find("APT::Sandbox::User");
+ if (toUser.empty() || toUser == "root")
+ return true;
+
+ // a lot can go wrong trying to drop privileges completely,
+ // so ideally we would like to verify that we have done it –
+ // but the verify asks for too much in case of fakeroot (and alike)
+ // [Specific checks can be overridden with dedicated options]
+ bool const VerifySandboxing = _config->FindB("APT::Sandbox::Verify", false);
+
+ // uid will be 0 in the end, but gid might be different anyway
+ uid_t const old_uid = getuid();
+ gid_t const old_gid = getgid();
+
+ if (old_uid != 0)
+ return true;
+
+ struct passwd *pw = getpwnam(toUser.c_str());
+ if (pw == NULL)
+ return _error->Error("No user %s, can not drop rights", toUser.c_str());
+
+ // Do not change the order here, it might break things
+ // Get rid of all our supplementary groups first
+ if (setgroups(1, &pw->pw_gid))
+ return _error->Errno("setgroups", "Failed to setgroups");
+
+ // Now change the group ids to the new user
+#ifdef HAVE_SETRESGID
+ if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0)
+ return _error->Errno("setresgid", "Failed to set new group ids");
+#else
+ if (setegid(pw->pw_gid) != 0)
+ return _error->Errno("setegid", "Failed to setegid");
+
+ if (setgid(pw->pw_gid) != 0)
+ return _error->Errno("setgid", "Failed to setgid");
+#endif
+
+ // Change the user ids to the new user
+#ifdef HAVE_SETRESUID
+ if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0)
+ return _error->Errno("setresuid", "Failed to set new user ids");
+#else
+ if (setuid(pw->pw_uid) != 0)
+ return _error->Errno("setuid", "Failed to setuid");
+ if (seteuid(pw->pw_uid) != 0)
+ return _error->Errno("seteuid", "Failed to seteuid");
+#endif
+
+ // disabled by default as fakeroot doesn't implement getgroups currently (#806521)
+ if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::Groups", false) == true)
+ {
+ // Verify that the user isn't still in any supplementary groups
+ long const ngroups_max = sysconf(_SC_NGROUPS_MAX);
+ std::unique_ptr<gid_t[]> gidlist(new gid_t[ngroups_max]);
+ if (unlikely(gidlist == NULL))
+ return _error->Error("Allocation of a list of size %lu for getgroups failed", ngroups_max);
+ ssize_t gidlist_nr;
+ if ((gidlist_nr = getgroups(ngroups_max, gidlist.get())) < 0)
+ return _error->Errno("getgroups", "Could not get new groups (%lu)", ngroups_max);
+ for (ssize_t i = 0; i < gidlist_nr; ++i)
+ if (gidlist[i] != pw->pw_gid)
+ return _error->Error("Could not switch group, user %s is still in group %d", toUser.c_str(), gidlist[i]);
+ }
+
+ // enabled by default as all fakeroot-lookalikes should fake that accordingly
+ if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::IDs", true) == true)
+ {
+ // Verify that gid, egid, uid, and euid changed
+ if (getgid() != pw->pw_gid)
+ return _error->Error("Could not switch group");
+ if (getegid() != pw->pw_gid)
+ return _error->Error("Could not switch effective group");
+ if (getuid() != pw->pw_uid)
+ return _error->Error("Could not switch user");
+ if (geteuid() != pw->pw_uid)
+ return _error->Error("Could not switch effective user");
+
+#ifdef HAVE_GETRESUID
+ // verify that the saved set-user-id was changed as well
+ uid_t ruid = 0;
+ uid_t euid = 0;
+ uid_t suid = 0;
+ if (getresuid(&ruid, &euid, &suid))
+ return _error->Errno("getresuid", "Could not get saved set-user-ID");
+ if (suid != pw->pw_uid)
+ return _error->Error("Could not switch saved set-user-ID");
+#endif
+
+#ifdef HAVE_GETRESGID
+ // verify that the saved set-group-id was changed as well
+ gid_t rgid = 0;
+ gid_t egid = 0;
+ gid_t sgid = 0;
+ if (getresgid(&rgid, &egid, &sgid))
+ return _error->Errno("getresuid", "Could not get saved set-group-ID");
+ if (sgid != pw->pw_gid)
+ return _error->Error("Could not switch saved set-group-ID");
+#endif
+ }
+
+ // disabled as fakeroot doesn't forbid (by design) (re)gaining root from unprivileged
+ if (VerifySandboxing == true || _config->FindB("APT::Sandbox::Verify::Regain", false) == true)
+ {
+ // Check that uid and gid changes do not work anymore
+ if (pw->pw_gid != old_gid && (setgid(old_gid) != -1 || setegid(old_gid) != -1))
+ return _error->Error("Could restore a gid to root, privilege dropping did not work");
+
+ if (pw->pw_uid != old_uid && (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
+ return _error->Error("Could restore a uid to root, privilege dropping did not work");
+ }
+
+ return true;
+}
+ /*}}}*/
projects / apt.git / blobdiff