tunables: Fix environment variable processing for setuid binaries (bz #21073)

Florian Weimer pointed out that we have three different kinds of
environment variables (and hence tunables):

1. Variables that are removed for setxid processes
2. Variables that are ignored in setxid processes but is passed on to
   child processes
3. Variables that are passed on to child processes all the time

Tunables currently only does (2) and (3) when it should be doing (1)
for MALLOC_CHECK_.  This patch enhances the is_secure flag in tunables
to an enum value that can specify which of the above three categories
the tunable (and its envvar alias) belongs to.

The default is for tunables to be in (1).  Hence, all of the malloc
tunables barring MALLOC_CHECK_ are explicitly specified to belong to
category (2).  There were discussions around abolishing category (2)
completely but we can do that as a separate exercise in 2.26.

Tested on x86_64 to verify that there are no regressions.

	[BZ #21073]
	* elf/dl-tunable-types.h (tunable_seclevel_t): New enum.
	* elf/dl-tunables.c (tunables_strdup): Remove.
	(get_next_env): Also return the previous envp.
	(parse_tunables): Erase tunables of category
	TUNABLES_SECLEVEL_SXID_ERASE.
	(maybe_enable_malloc_check): Make MALLOC_CHECK_
	TUNABLE_SECLEVEL_NONE if /etc/setuid-debug is accessible.
	(__tunables_init)[TUNABLES_FRONTEND ==
	TUNABLES_FRONTEND_valstring]: Update GLIBC_TUNABLES envvar
	after parsing.
	[TUNABLES_FRONTEND != TUNABLES_FRONTEND_valstring]: Erase
	tunable envvars of category TUNABLES_SECLEVEL_SXID_ERASE.
	* elf/dl-tunables.h (struct _tunable): Change member is_secure
	to security_level.
	* elf/dl-tunables.list: Add security_level annotations for all
	tunables.
	* scripts/gen-tunables.awk: Recognize and generate enum values
	for security_level.
	* elf/tst-env-setuid.c: New test case.
	* elf/tst-env-setuid-tunables: new test case.
	* elf/Makefile (tests-static): Add them.

1 files changed, 60 insertions, 0 deletions

diff --git a/elf/tst-env-setuid-tunables.c b/elf/tst-env-setuid-tunables.c
new file mode 100644
index 0000000000..a563f69972
--- /dev/null
+++ b/elf/tst-env-setuid-tunables.c
@@ -0,0 +1,60 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Verify that tunables correctly filter out unsafe tunables like
+   glibc.malloc.check and glibc.malloc.mmap_threshold but also retain
+   glibc.malloc.mmap_threshold in an unprivileged child.  */
+
+#define test_parent test_parent_tunables
+#define test_child test_child_tunables
+
+static int test_child_tunables (void);
+static int test_parent_tunables (void);
+
+#include "tst-env-setuid.c"
+
+#define CHILD_VALSTRING_VALUE "glibc.malloc.mmap_threshold=4096"
+#define PARENT_VALSTRING_VALUE \
+  "glibc.malloc.check=2:glibc.malloc.mmap_threshold=4096"
+
+static int
+test_child_tunables (void)
+{
+  const char *val = getenv ("GLIBC_TUNABLES");
+
+  if (val != NULL && strcmp (val, CHILD_VALSTRING_VALUE) == 0)
+    return 0;
+
+  if (val != NULL)
+    printf ("Unexpected GLIBC_TUNABLES VALUE %s\n", val);
+
+  return 1;
+}
+
+static int
+test_parent_tunables (void)
+{
+  const char *val = getenv ("GLIBC_TUNABLES");
+
+  if (val != NULL && strcmp (val, PARENT_VALSTRING_VALUE) == 0)
+    return 0;
+
+  if (val != NULL)
+    printf ("Unexpected GLIBC_TUNABLES VALUE %s\n", val);
+
+  return 1;
+}