Add function getlocalbase() to libutil.

This function returns the path to the local software base directory, by
default "/usr/local" (or the value of _PATH_LOCALBASE in include/paths.h
when building the world).

The value returned can be overridden by 2 methods:

- the LOCALBASE environment variable (ignored by SUID programs)
- else a non-default user.localbase sysctl value

Reviewed by:	hps (earlier version)
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D27236

4 files changed, 178 insertions, 2 deletions

diff --git a/lib/libutil/Makefile b/lib/libutil/Makefile
index 5ea2addd5d34..df3fb622b374 100644
--- a/lib/libutil/Makefile
+++ b/lib/libutil/Makefile
@@ -12,7 +12,8 @@ PACKAGE=	runtime
 LIB=	util
 SHLIB_MAJOR= 9
 
-SRCS=	_secure_path.c auth.c expand_number.c flopen.c fparseln.c gr_util.c \
+SRCS=	_secure_path.c auth.c expand_number.c flopen.c fparseln.c \
+	getlocalbase.c  gr_util.c \
 	hexdump.c humanize_number.c kinfo_getfile.c \
 	kinfo_getallproc.c kinfo_getproc.c kinfo_getvmmap.c \
 	kinfo_getvmobject.c kld.c \
@@ -30,7 +31,7 @@ CFLAGS+= -DINET6
 
 CFLAGS+= -I${.CURDIR} -I${SRCTOP}/lib/libc/gen/
 
-MAN+=	expand_number.3 flopen.3 fparseln.3 hexdump.3 \
+MAN+=	expand_number.3 flopen.3 fparseln.3 getlocalbase.3 hexdump.3 \
 	humanize_number.3 kinfo_getallproc.3 kinfo_getfile.3 \
 	kinfo_getproc.3 kinfo_getvmmap.3 kinfo_getvmobject.3 kld.3 \
 	login_auth.3 login_cap.3 \
diff --git a/lib/libutil/getlocalbase.3 b/lib/libutil/getlocalbase.3
new file mode 100644
index 000000000000..ed0a4a3c1226
--- /dev/null
+++ b/lib/libutil/getlocalbase.3
@@ -0,0 +1,99 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+.\"
+.\" Copyright 2020 Scott Long
+.\" Copyright 2020 Stefan Eßer
+.\"
+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd November 18, 2020
+.Dt GETLOCALBASE 3
+.Os
+.Sh NAME
+.Nm getlocalbase
+.Nd "return the path to the local software directory"
+.Sh LIBRARY
+.Lb libutil
+.Sh SYNOPSIS
+.In libutil.h
+.Ft const char*
+.Fn getlocalbase "void"
+.Sh DESCRIPTION
+The
+.Fn getlocalbase
+function returns the path to the local software base directory.
+Normally this is the
+.Pa /usr/local
+directory.
+First the
+.Ev LOCALBASE
+environment variable is checked.
+If that does not exist then the
+.Va user.localbase
+sysctl is checked.
+If that also does not exist then the value of the
+.Dv _PATH_LOCALBASE
+compile-time variable is used.
+If that is undefined then the default of
+.Pa /usr/local
+is used.
+.Pp
+The value returned by the
+.Fn getlocalbase
+function shall not be modified.
+.Sh IMPLEMENTATION NOTES
+Calls to
+.Fn getlocalbase
+will perform a setugid check on the running binary before checking the
+environment.
+.Sh RETURN VALUES
+The
+.Fn getlocalbase
+function always succeeds and returns a pointer to a string, whose length
+may exceed MAXPATHLEN if it has been derived from the environment variable
+LOCALBASE.
+No length checks are performed on the result.
+.Sh ENVIRONMENT
+The
+.Fn getlocalbase
+library function retrieves the
+.Ev LOCALBASE
+environment variable.
+.Sh ERRORS
+The
+.Fn getlocalbase
+function always succeeds.
+.Sh SEE ALSO
+.Xr env 1 ,
+.Xr src.conf 5 ,
+.Xr sysctl 8
+.Sh HISTORY
+The
+.Nm
+library function first appeared in
+.Fx 13.0 .
+.Sh AUTHORS
+This
+manual page was written by
+.An Scott Long Aq Mt scottl@FreeBSD.org and Stefan Eßer Aq Mt se@FreeBSD.org .
diff --git a/lib/libutil/getlocalbase.c b/lib/libutil/getlocalbase.c
new file mode 100644
index 000000000000..3d6bcc067391
--- /dev/null
+++ b/lib/libutil/getlocalbase.c
@@ -0,0 +1,74 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2020 Stefan Eßer <se@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 REGENTS 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 REGENTS 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.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/sysctl.h>
+#include <sys/limits.h>
+#include <stdlib.h>
+#include <paths.h>
+#include <libutil.h>
+#include <unistd.h>
+
+#ifndef _PATH_LOCALBASE
+#define _PATH_LOCALBASE "/usr/local"
+#endif
+
+const char *
+getlocalbase(void)
+{
+	static const int localbase_oid[2] = {CTL_USER, USER_LOCALBASE};
+	char *tmppath;
+	size_t tmplen;
+	static const char *localbase = NULL;
+
+	if (issetugid() == 0) {
+		tmppath = getenv("LOCALBASE");
+		if (tmppath != NULL && tmppath[0] != '\0')
+			return (tmppath);
+	}
+	if (sysctl(localbase_oid, 2, NULL, &tmplen, NULL, 0) == 0 &&
+	    (tmppath = malloc(tmplen)) != NULL && 
+	    sysctl(localbase_oid, 2, tmppath, &tmplen, NULL, 0) == 0) {
+		/*
+		 * Check for some other thread already having 
+		 * set localbase - this should use atomic ops.
+		 * The amount of memory allocated above may leak,
+		 * if a parallel update in another thread is not
+		 * detected and the non-NULL pointer is overwritten.
+		 */
+		if (tmppath[0] != '\0' &&
+		    (volatile const char*)localbase == NULL)
+			localbase = tmppath;
+		else
+			free((void*)tmppath);
+		return (localbase);
+	}
+	return (_PATH_LOCALBASE);
+}
diff --git a/lib/libutil/libutil.h b/lib/libutil/libutil.h
index 2ac5e975a2d7..bb96b2caa502 100644
--- a/lib/libutil/libutil.h
+++ b/lib/libutil/libutil.h
@@ -98,6 +98,8 @@ int	flopen(const char *_path, int _flags, ...);
 int	flopenat(int _dirfd, const char *_path, int _flags, ...);
 int	forkpty(int *_amaster, char *_name,
 	    struct termios *_termp, struct winsize *_winp);
+const char *
+	getlocalbase(void);
 void	hexdump(const void *_ptr, int _length, const char *_hdr, int _flags);
 int	humanize_number(char *_buf, size_t _len, int64_t _number,
 	    const char *_suffix, int _scale, int _flags);