On 11/18/20, Stefan Eßer <s...@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 sco...@freebsd.org and Stefan Eßer Aq Mt
> s...@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 <s...@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).
Also the kernel counter part completely unnecessarily comes with a
static 1KB buffer to hold what typically is going to be nothing. This
should also be allocated as needed. Worst case you can add a trivial
lock around it.
> + /*
> + * 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);
> +}
>
> Modified: head/lib/libutil/libutil.h
> ==============================================================================
> --- head/lib/libutil/libutil.h Wed Nov 18 19:35:30 2020
> (r367812)
> +++ head/lib/libutil/libutil.h Wed Nov 18 19:44:30 2020
> (r367813)
> @@ -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);
>
--
Mateusz Guzik <mjguzik gmail.com>
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