libc: add clearenv function

The clearenv(3) function allows us to clear all environment
variable in one shot. This may be useful for security programs that
want to control the environment or what variables are passed to new
spawned programs.

Reviewed by:	scf, markj (secteam), 0mp (manpages)
Differential Revision:	https://reviews.freebsd.org/D28223

include/stdlib.h

@@ -283,6 +283,8 @@ int	 cgetset(const char *);
 int	 cgetstr(char *, const char *, char **);
 int	 cgetustr(char *, const char *, char **);
 
+int	 clearenv(void);
+
 int	 daemon(int, int);
 int	 daemonfd(int, int);
 char	*devname(__dev_t, __mode_t);

lib/libc/stdlib/Makefile.inc

@@ -46,7 +46,8 @@ MAN+=	a64l.3 abort.3 abs.3 alloca.3 atexit.3 atof.3 \
 MLINKS+=a64l.3 l64a.3 a64l.3 l64a_r.3
 MLINKS+=atol.3 atoll.3
 MLINKS+=exit.3 _Exit.3
-MLINKS+=getenv.3 putenv.3 getenv.3 setenv.3 getenv.3 unsetenv.3
+MLINKS+=getenv.3 clearenv.3 getenv.3 putenv.3 getenv.3 setenv.3 \
+	getenv.3 unsetenv.3
 MLINKS+=getopt_long.3 getopt_long_only.3
 MLINKS+=hcreate.3 hdestroy.3 hcreate.3 hsearch.3
 MLINKS+=hcreate.3 hcreate_r.3 hcreate.3 hdestroy_r.3 hcreate.3 hsearch_r.3

lib/libc/stdlib/Symbol.map

@@ -128,6 +128,10 @@ FBSD_1.6 {
 	srand;
 };
 
+FBSD_1.7 {
+	clearenv;
+};
+
 FBSDprivate_1.0 {
 	__system;
 	_system;

lib/libc/stdlib/getenv.3

@@ -32,10 +32,11 @@
 .\"     @(#)getenv.3	8.2 (Berkeley) 12/11/93
 .\" $FreeBSD$
 .\"
-.Dd June 20, 2007
+.Dd November 7, 2021
 .Dt GETENV 3
 .Os
 .Sh NAME
+.Nm clearenv ,
 .Nm getenv ,
 .Nm putenv ,
 .Nm setenv ,
@@ -45,6 +46,8 @@
 .Lb libc
 .Sh SYNOPSIS
 .In stdlib.h
+.Ft int
+.Fn clearenv "void"
 .Ft char *
 .Fn getenv "const char *name"
 .Ft int
@@ -59,6 +62,14 @@ host
 .Em environment list .
 .Pp
 The
+.Fn clearenv
+function clears all environment variables.
+New variables can be added using
+.Fn setenv
+and
+.Fn putenv .
+.Pp
+The
 .Fn getenv
 function obtains the current value of the environment variable,
 .Fa name .
@@ -128,7 +139,7 @@ is not in the current environment,
 .Dv NULL
 is returned.
 .Pp
-.Rv -std setenv putenv unsetenv
+.Rv -std clearenv setenv putenv unsetenv
 .Sh ERRORS
 .Bl -tag -width Er
 .It Bq Er EINVAL
@@ -211,6 +222,11 @@ This was changed to use
 as the memory location of the ``name=value'' pair to follow the
 .Tn POSIX
 specification.
+.Pp
+The
+.Fn clearenv
+was added in
+.Fx 14 .
 .Sh BUGS
 Successive calls to
 .Fn setenv

lib/libc/stdlib/getenv.c

@@ -691,3 +691,28 @@ unsetenv(const char *name)
 
 	return (0);
 }
+
+/*
+ * Unset all variable by flagging them as inactive.  No variable is
+ * ever freed.
+ */
+int
+clearenv(void)
+{
+	int ndx;
+
+	/* Initialize environment. */
+	if (__merge_environ() == -1 || (envVars == NULL && __build_env() == -1))
+		return (-1);
+
+	/* Remove from the end to not shuffle memory too much. */
+	for (ndx = envVarsTotal - 1; ndx >= 0; ndx--) {
+		envVars[ndx].active = false;
+		if (envVars[ndx].putenv)
+			__remove_putenv(ndx);
+	}
+
+	__rebuild_environ(0);
+
+	return (0);
+}

lib/libc/tests/stdlib/Makefile

@@ -2,6 +2,7 @@
 
 .include <src.opts.mk>
 
+ATF_TESTS_C+=		clearenv_test
 ATF_TESTS_C+=		dynthr_test
 ATF_TESTS_C+=		heapsort_test
 ATF_TESTS_C+=		mergesort_test

lib/libc/tests/stdlib/clearenv_test.c

@@ -0,0 +1,176 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 2021 Mariusz Zaborski <oshogbo@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * Test for clearenv(3) routine.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <atf-c.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define TEST_VARIABLE		"TEST_VAR"
+#define TEST_SYSTEM_VARIABLE	"PWD"
+
+extern char **environ;
+
+void
+create_multiple_variables(int num)
+{
+	char name[64];
+	char value[64];
+	int i;
+
+	for (i = 0; i < num; i++) {
+		snprintf(name, sizeof(name), "%s_%d", TEST_VARIABLE, i);
+		snprintf(value, sizeof(value), "%d", i);
+		ATF_CHECK(getenv(name) == NULL);
+		ATF_CHECK(setenv(name, value, 0) != -1);
+		ATF_CHECK_STREQ(getenv(name), value);
+	}
+}
+
+void
+check_if_nulled_variables(int num)
+{
+	char name[64];
+	int i;
+
+	for (i = 0; i < num; i++) {
+		snprintf(name, sizeof(name), "%s_%d", TEST_VARIABLE, i);
+		ATF_CHECK(getenv(name) == NULL);
+	}
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__single_var_test);
+ATF_TC_BODY(clearenv__single_var_test, tc)
+{
+
+	ATF_CHECK(setenv(TEST_VARIABLE, "true", 0) != -1);
+	ATF_CHECK_STREQ(getenv(TEST_VARIABLE), "true");
+	ATF_CHECK(clearenv() == 0);
+	ATF_CHECK(getenv(TEST_VARIABLE) == NULL);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__multiple_vars_test);
+ATF_TC_BODY(clearenv__multiple_vars_test, tc)
+{
+
+	create_multiple_variables(10);
+	ATF_CHECK(clearenv() == 0);
+	check_if_nulled_variables(10);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__recreated_vars_test);
+ATF_TC_BODY(clearenv__recreated_vars_test, tc)
+{
+
+	create_multiple_variables(10);
+	ATF_CHECK(clearenv() == 0);
+	check_if_nulled_variables(10);
+	create_multiple_variables(10);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__system_var_test);
+ATF_TC_BODY(clearenv__system_var_test, tc)
+{
+
+	ATF_CHECK(getenv(TEST_SYSTEM_VARIABLE) != NULL);
+	ATF_CHECK(clearenv() == 0);
+	ATF_CHECK(getenv(TEST_SYSTEM_VARIABLE) == NULL);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__recreated_system_var_test);
+ATF_TC_BODY(clearenv__recreated_system_var_test, tc)
+{
+
+	ATF_CHECK(getenv(TEST_SYSTEM_VARIABLE) != NULL);
+	ATF_CHECK(clearenv() == 0);
+	ATF_CHECK(getenv(TEST_SYSTEM_VARIABLE) == NULL);
+	ATF_CHECK(setenv(TEST_SYSTEM_VARIABLE, "test", 0) != -1);
+	ATF_CHECK_STREQ(getenv(TEST_SYSTEM_VARIABLE), "test");
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__double_clear_vars);
+ATF_TC_BODY(clearenv__double_clear_vars, tc)
+{
+
+	create_multiple_variables(10);
+	ATF_CHECK(clearenv() == 0);
+	check_if_nulled_variables(10);
+	ATF_CHECK(clearenv() == 0);
+	check_if_nulled_variables(10);
+	create_multiple_variables(10);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__environ_null);
+ATF_TC_BODY(clearenv__environ_null, tc)
+{
+
+	ATF_CHECK(clearenv() == 0);
+	ATF_CHECK(environ == NULL);
+}
+
+ATF_TC_WITHOUT_HEAD(clearenv__putenv_vars);
+ATF_TC_BODY(clearenv__putenv_vars, tc)
+{
+	char buf[64], ref[64];
+
+	snprintf(buf, sizeof(buf), "%s=1", TEST_VARIABLE);
+	strcpy(ref, buf);
+
+	ATF_CHECK(getenv(TEST_VARIABLE) == NULL);
+	ATF_CHECK(putenv(buf) != -1);
+	ATF_CHECK(strcmp(getenv(TEST_VARIABLE), "1") == 0);
+
+	ATF_CHECK(clearenv() == 0);
+
+	ATF_CHECK(getenv(TEST_VARIABLE) == NULL);
+	ATF_CHECK(strcmp(buf, ref) == 0);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, clearenv__single_var_test);
+	ATF_TP_ADD_TC(tp, clearenv__multiple_vars_test);
+	ATF_TP_ADD_TC(tp, clearenv__recreated_vars_test);
+
+	ATF_TP_ADD_TC(tp, clearenv__system_var_test);
+	ATF_TP_ADD_TC(tp, clearenv__recreated_system_var_test);
+
+	ATF_TP_ADD_TC(tp, clearenv__double_clear_vars);
+	ATF_TP_ADD_TC(tp, clearenv__environ_null);
+
+	ATF_TP_ADD_TC(tp, clearenv__putenv_vars);
+
+	return (atf_no_error());
+}