svn commit: r367813 - head/lib/libutil

Wed Nov 18 21:46:44 UTC 2020

On 18 Nov 2020, at 21:40, Mateusz Guzik <mjguzik at gmail.com> wrote:
> 
> On 11/18/20, Stefan Eßer <se at freebsd.org> wrote:
>> Author: se
>> Date: Wed Nov 18 19:44:30 2020
>> New Revision: 367813
>> URL: https://svnweb.freebsd.org/changeset/base/367813
>> 
>> Log:
>>  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
>> 
>> Added:
>>  head/lib/libutil/getlocalbase.3   (contents, props changed)
>>  head/lib/libutil/getlocalbase.c   (contents, props changed)
>> Modified:
>>  head/lib/libutil/Makefile
>>  head/lib/libutil/libutil.h
>> 
>> Modified: head/lib/libutil/Makefile
>> ==============================================================================
>> --- head/lib/libutil/Makefile	Wed Nov 18 19:35:30 2020	(r367812)
>> +++ head/lib/libutil/Makefile	Wed Nov 18 19:44:30 2020	(r367813)
>> @@ -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 \
>> 
>> Added: head/lib/libutil/getlocalbase.3
>> ==============================================================================
>> --- /dev/null	00:00:00 1970	(empty, because file is newly added)
>> +++ head/lib/libutil/getlocalbase.3	Wed Nov 18 19:44:30 2020	(r367813)
>> @@ -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 at FreeBSD.org and Stefan Eßer Aq Mt
>> se at FreeBSD.org .
>> 
>> Added: head/lib/libutil/getlocalbase.c
>> ==============================================================================
>> --- /dev/null	00:00:00 1970	(empty, because file is newly added)
>> +++ head/lib/libutil/getlocalbase.c	Wed Nov 18 19:44:30 2020	(r367813)
>> @@ -0,0 +1,74 @@
>> +/*-
>> + * SPDX-License-Identifier: BSD-2-Clause
>> + *
>> + * Copyright 2020 Stefan Eßer <se at 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};
> 
> There is no use for this to be static.
> 
>> +	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) {
> 
> Apart from the concurrency issue mentioned in the comment this is just
> very wasteful. Instead you can have a small local buffer, say 128
> bytes and pass that to be populated. The sysctl handler than can
> populate that and return an error if the size is too small. I don't
> know if sysclt api allows it to return the set size as it is. Worst
> case you can just retry with a bigger malloced buffer.
> 
> Once you get the result you can malloc a buffer and
> atomic_cmpset_rel_ptr localbase to point to it. If this fails, another
> thread got the result, you free your buffer and return (localbase).

That would still need to be an acquire load (if using C11 atomics,
technically consume is fine, but in practice is no more efficient).

Jess