Linux sandbox: save full list of SUID unsafe environment variables.

sandbox/linux/suid/suid_unsafe_environment_variables.h

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This is a list of environment variables which the ELF loader unsets when
+// loading a SUID binary. Because they are unset rather than just ignored, they
+// aren't passed to child processes of SUID processes either.
+//
+// We need to save these environment variables before running a SUID sandbox
+// and restore them before running child processes (but after dropping root).
+//
+// List gathered from glibc sources (00ebd7ed58df389a78e41dece058048725cb585e):
+//   sysdeps/unix/sysv/linux/i386/dl-librecon.h
+//   sysdeps/generic/unsecvars.h
+
+static const char* kSUIDUnsafeEnvironmentVariables[] = {
+  "LD_AOUT_LIBRARY_PATH",
+  "LD_AOUT_PRELOAD",
+  "GCONV_PATH",
+  "GETCONF_DIR",
+  "HOSTALIASES",
+  "LD_AUDIT",
+  "LD_DEBUG",
+  "LD_DEBUG_OUTPUT",
+  "LD_DYNAMIC_WEAK",
+  "LD_LIBRARY_PATH",
+  "LD_ORIGIN_PATH",
+  "LD_PRELOAD",
+  "LD_PROFILE",
+  "LD_SHOW_AUXV",
+  "LD_USE_LOAD_BIAS",
+  "LOCALDOMAIN",
+  "LOCPATH",
+  "MALLOC_TRACE",
+  "NIS_PATH",
+  "NLSPATH",
+  "RESOLV_HOST_CONF",
+  "RES_OPTIONS",
+  "TMPDIR",
+  "TZDIR",
+  NULL,
+};
+
+// Return a malloc allocated string containing the 'saved' environment variable
+// name for a given environment variable.
+static inline char* SandboxSavedEnvironmentVariable(const char* envvar) {
+  const size_t envvar_len = strlen(envvar);
+  const size_t saved_envvarlen = envvar_len + 1 /* NUL terminator */ +
+                                 8 /* strlen("SANDBOX_") */;

[Evan Martin, 2009/07/17 21:10:57]

This seems like a ton of effort to go through.  Why not just
  return std::string("SANDBOX_") + envvar;

Eliminates manual memory management on the callee side oto.

[agl, 2009/07/17 21:35:09]

I'm currently sticking to the idea that the sandbox is pure-C99 code (although
we do compile as C++ because our build system is setup that way).

+  char* const saved_envvar = (char*) malloc(saved_envvarlen);
+  if (!saved_envvar)
+    return NULL;
+
+  memcpy(saved_envvar, "SANDBOX_", 8);
+  memcpy(saved_envvar + 8, envvar, envvar_len);
+  saved_envvar[8 + envvar_len] = 0;
+
+  return saved_envvar;
+}