1 files changed, 109 insertions, 0 deletions
diff --git a/capabilities.cc b/capabilities.cc
new file mode 100644
index 0000000..e073d2c
--- /dev/null
+++ b/capabilities.cc
@@ -0,0 +1,109 @@
+/*
+ * This file is part of PowerDNS or dnsdist.
+ * Copyright -- PowerDNS.COM B.V. and its contributors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * In addition, for the avoidance of any doubt, permission is granted to
+ * link this program with OpenSSL and to (re)distribute the binaries
+ * produced as the result of such linking.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+
+#include <cstring>
+#include <stdexcept>
+
+#ifdef HAVE_LIBCAP
+#include <sys/capability.h>
+#include <sys/prctl.h>
+#endif
+
+#include "capabilities.hh"
+#include "misc.hh"
+
+bool dropCapabilities(std::set<std::string> capabilitiesToKeep)
+{
+#ifdef HAVE_LIBCAP
+   cap_t caps = cap_get_proc();
+   if (caps != nullptr) {
+     cap_clear(caps);
+
+     if (!capabilitiesToKeep.empty()) {
+       std::vector<cap_value_t> toKeep;
+       toKeep.reserve(capabilitiesToKeep.size());
+
+       for (const auto& capToKeep : capabilitiesToKeep) {
+         cap_value_t value;
+         int res = cap_from_name(capToKeep.c_str(), &value);
+         if (res != 0) {
+           cap_free(caps);
+           throw std::runtime_error("Unable to convert capability name '" + capToKeep + "': " + stringerror());
+         }
+         toKeep.push_back(value);
+       }
+
+       if (cap_set_flag(caps, CAP_EFFECTIVE, toKeep.size(), toKeep.data(), CAP_SET) != 0) {
+         cap_free(caps);
+         throw std::runtime_error("Unable to set effective flag capabilities: " + stringerror());
+       }
+
+       if (cap_set_flag(caps, CAP_PERMITTED, toKeep.size(), toKeep.data(), CAP_SET) != 0) {
+         cap_free(caps);
+         throw std::runtime_error("Unable to set permitted flag capabilities: " + stringerror());
+       }
+     }
+
+     if (cap_set_proc(caps) != 0) {
+       cap_free(caps);
+       if (errno == EPERM) {
+         return false;
+       }
+       throw std::runtime_error("Unable to drop capabilities: " + stringerror());
+     }
+
+     cap_free(caps);
+     return true;
+   }
+#endif /* HAVE_LIBCAP */
+   return false;
+}
+
+bool dropCapabilitiesAfterSwitchingIDs()
+{
+#ifdef HAVE_LIBCAP
+#ifdef PR_SET_KEEPCAPS
+  if (prctl(PR_SET_KEEPCAPS, 0, 0, 0, 0) == 0) {
+    return true;
+  }
+#endif /* PR_SET_KEEPCAPS */
+  return false;
+#else
+  return false;
+#endif /* HAVE_LIBCAP */
+}
+
+bool keepCapabilitiesAfterSwitchingIDs()
+{
+#ifdef HAVE_LIBCAP
+#ifdef PR_SET_KEEPCAPS
+  if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) == 0) {
+    return true;
+  }
+#endif /* PR_SET_KEEPCAPS */
+  return false;
+#else
+  return false;
+#endif /* HAVE_LIBCAP */
+}