libcasper: introduce cap_fileargs service

cap_fileargs is a Casper service which helps to sandbox applications that need
access to the filesystem namespace. The main purpose of the service is to make
easy to capsicumize applications that works on multiple files passed in argv.

We have a couple example of using it but we still treat this service as an
experimental one.

Reviewed by:	emsate (previous version), jonathan (partially)
Discussed with:	many
Differential Revision:	https://reviews.freebsd.org/D14407

lib/libcasper/services/Makefile

@@ -3,6 +3,7 @@
 .include <src.opts.mk>
 
 SUBDIR=		cap_dns
+SUBDIR+=	cap_fileargs
 SUBDIR+=	cap_grp
 SUBDIR+=	cap_pwd
 SUBDIR+=	cap_random

lib/libcasper/services/cap_fileargs/Makefile

@@ -0,0 +1,35 @@
+# $FreeBSD$
+
+SHLIBDIR?=	/lib/casper
+
+.include <src.opts.mk>
+
+PACKAGE=libcasper
+
+SHLIB_MAJOR=	1
+INCSDIR?=	${INCLUDEDIR}/casper
+
+.if ${MK_CASPER} != "no"
+SHLIB=	cap_fileargs
+
+SRCS=	cap_fileargs.c
+.endif
+
+INCS=	cap_fileargs.h
+
+LIBADD=	nv
+
+CFLAGS+=-I${.CURDIR}
+
+MAN+=	cap_fileargs.3
+
+MLINKS+=cap_fileargs.3 libcap_fileargs.3
+MLINKS+=cap_fileargs.3 fileargs_cinit.3
+MLINKS+=cap_fileargs.3 fileargs_cinitnv.3
+MLINKS+=cap_fileargs.3 fileargs_fopen.3
+MLINKS+=cap_fileargs.3 fileargs_free.3
+MLINKS+=cap_fileargs.3 fileargs_init.3
+MLINKS+=cap_fileargs.3 fileargs_initnv.3
+MLINKS+=cap_fileargs.3 fileargs_open.3
+
+.include <bsd.lib.mk>

lib/libcasper/services/cap_fileargs/cap_fileargs.3

@@ -0,0 +1,241 @@
+.\" Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
+.\" All rights reserved.
+.\"
+.\" 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 AUTHORS 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 AUTHORS 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 12, 2018
+.Dt CAP_FILEARGS 3
+.Os
+.Sh NAME
+.Nm fileargs_cinit ,
+.Nm fileargs_cinitnv ,
+.Nm fileargs_init ,
+.Nm fileargs_initnv ,
+.Nm fileargs_free ,
+.Nm fileargs_open ,
+.Nm fileargs_fopen
+.Nd "library for handling files in capability mode"
+.Sh LIBRARY
+.Lb libcap_fileargs
+.Sh SYNOPSIS
+.In sys/nv.h
+.In libcasper.h
+.In casper/cap_fileargs.h
+.Ft "fileargs_t *"
+.Fn fileargs_init "int argc" "char *argv[]" "int flags" "mode_t mode" "cap_rights_t *rightsp"
+.Ft "fileargs_t *"
+.Fn fileargs_cinit "cap_channel_t *cas" "int argc" "char *argv[]" "int flags" "mode_t mode" "cap_rights_t *rightsp"
+.Ft "fileargs_t *"
+.Fn fileargs_cinitnv "cap_channel_t *cas" "nvlist_t *limits"
+.Ft "fileargs_t *"
+.Fn fileargs_initnv "nvlist_t *limits"
+.Ft "void"
+.Fn fileargs_free "fileargs_t *fa"
+.Ft "int"
+.Fn fileargs_open "fileargs_t *fa" "const char *name"
+.Ft "FILE *"
+.Fn fileargs_fopen "fileargs_t *fa" "const char *name" "const char *mode"
+.Sh DESCRIPTION
+The library is used to simplify Capsicumizing a tools that are using file system.
+Idea behind the library is that we are passing a remaining
+.Fa argc
+and
+.Fa argv
+which contains a list of files that should be open for this program.
+The library will create a service that will serve those files.
+.Pp
+The function
+.Fn fileargs_init
+create a service to the
+.Nm system.fileargs .
+The
+.Fa argv
+contains a list of files that should be opened.
+The argument can be set to
+.Dv NULL
+which will not create a service and all files will be prohibited to be opened.
+The
+.Fa argc
+argument contains a number of passed files.
+The
+.Fa flags
+argument limits opened files for either execution or reading and/or writing.
+The
+.Fa mode
+argument tells which what mode file should be created if the
+.Dv O_CREATE
+flag is present .
+For more details of the
+.Fa flags
+and
+.Fa mode
+arguments see
+.Xr open 2 .
+The
+.Fa rightsp
+argument contains a list of the capability rights which file should be limited to.
+For more details of the capability rights see
+.Xr cap_rights_init 3 .
+.Pp
+The function
+.Fn fileargs_cinit
+is equivalent to
+.Fn fileargs_init
+except that the connection to the Casper needs to be provided.
+.Pp
+The functions
+.Fn fileargs_ininv
+and
+.Fn fileargs_cininv
+are respectively equivalent to
+.Fn fileargs_init
+and
+.Fn fileargs_cinit
+expect that all arguments all provided as
+.Xr nvlist 9 .
+For details see
+.Sx LIMITS .
+.Pp
+The
+.Fa fileargs_free
+close connection to the
+.Nm system.filerags
+service and free are structures.
+The function handle
+.Dv NULL
+argument.
+.Pp
+The functions
+.Fn fileargs_open
+and
+.Fn fileargs_fopen
+are respectively equivalent to
+.Xr open 2
+and
+.Xr fopen 3
+expect that all arguments are fetched from the
+.Va fileargs_t
+structure.
+.Sh LIMITS
+This section describe which values and types should be used to pass arguments to the
+.Fa system.filerags
+through the
+.Fn fileargs_ininv
+and
+.Fn fileargs_cinit
+functions.
+The
+.Xr nvlist 9
+for that functions must contain the following values and types:
+.Bl -ohang -offset indent
+.It flags ( NV_TYPE_NUMBER )
+The
+.Va flags
+limits opened files for either execution or reading and/or writing.
+.It mode (NV_TYPE_NUMBER)
+If in the
+.Va flags
+argument the
+.Dv O_CREATE
+flag was defined the
+.Xr nvlist 9
+must contain the
+.Va mode .
+The
+.Va mode
+argument tells which what mode file should be created.
+.El
+.Pp
+The
+.Xr nvlist 9
+for that functions may contain the following values and types:
+.Bl -ohang -offset indent
+.It cap_rights ( NV_TYPE_BINARY )
+The
+.Va cap_rights
+argument contains a list of the capability rights which file should be limited to.
+.It ( NV_TYPE_NULL )
+Any number of
+.Dv NV_TYPE_NULL
+where the name of the element is name of the file which can be opened.
+.Sh EXAMPLES
+The following example first parse some options and then create the
+.Nm system.filerags
+service with remaining arguments.
+.Bd -literal
+int ch, fd, i;
+cap_rights_t rights;
+fileargs_t *fa;
+
+while ((ch = getopt(argc, argv, "h")) != -1) {
+	switch (ch) {
+		case 'h':
+		default:
+			usage();
+	}
+}
+
+argc -= optind;
+argv += optind;
+
+/* Create capability to the system.fileargs service. */
+fa = fileargs_init(argc, argv, O_RDONLY, 0,
+    cap_rights_init(&rights, CAP_READ));
+if (fa == NULL)
+	err(1, "unable to open system.fileargs service");
+
+/* Enter capability mode sandbox. */
+if (cap_enter() < 0 && errno != ENOSYS)
+	err(1, "unable to enter capability mode");
+
+/* Open files. */
+for (i = 0; i < argc; i++) {
+	fd = fileargs_open(fa, argv[i]);
+	if (fd < 0)
+		err(1, "unable to open file %s", argv[i]);
+	printf("File %s opened in capability mode\n", argv[i]);
+	close(fd);
+}
+
+fileargs_free(fa);
+.Ed
+.Sh SEE ALSO
+.Xr cap_enter 2 ,
+.Xr open 2 ,
+.Xr cap_rights_init 3 ,
+.Xr err 3 ,
+.Xr fopen 3,
+.Xr getopt 3,
+.Xr capsicum 4 ,
+.Xr nv 9
+.Sh BUGS
+The
+.Lb cap_fileargs
+included in
+.Fx
+is considered experimental, and should not be deployed in production
+environments without careful consideration of the risks associated with
+the use of experimental operating system features.
+.Sh AUTHORS
+.An Mariusz Zaborski Aq Mt oshogbo@FreeBSD.org

lib/libcasper/services/cap_fileargs/cap_fileargs.c

@@ -0,0 +1,505 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
+ * All rights reserved.
+ *
+ * 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 AUTHORS 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 AUTHORS 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/types.h>
+#include <sys/capsicum.h>
+#include <sys/sysctl.h>
+#include <sys/cnv.h>
+#include <sys/dnv.h>
+#include <sys/nv.h>
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <libcasper.h>
+#include <libcasper_service.h>
+
+#include "cap_fileargs.h"
+
+#define CACHE_SIZE	128
+
+#define FILEARGS_MAGIC	0xFA00FA00
+
+struct fileargs {
+	uint32_t	 fa_magic;
+	nvlist_t	*fa_cache;
+	cap_channel_t	*fa_chann;
+	int		 fa_fdflags;
+};
+
+static int
+fileargs_get_cache(fileargs_t *fa, const char *name)
+{
+	int fd;
+	const nvlist_t *nvl;
+	nvlist_t *tnvl;
+
+	assert(fa != NULL);
+	assert(fa->fa_magic == FILEARGS_MAGIC);
+	assert(name != NULL);
+
+	if (fa->fa_cache == NULL)
+		return (-1);
+
+	if ((fa->fa_fdflags & O_CREAT) != 0)
+		return (-1);
+
+	nvl = dnvlist_get_nvlist(fa->fa_cache, name, NULL);
+	if (nvl == NULL)
+		return (-1);
+
+	tnvl = nvlist_take_nvlist(fa->fa_cache, name);
+	fd = nvlist_take_descriptor(tnvl, "fd");
+	nvlist_destroy(tnvl);
+
+	if ((fa->fa_fdflags & O_CLOEXEC) != O_CLOEXEC) {
+		if (fcntl(fd, F_SETFD, fa->fa_fdflags) == -1) {
+			close(fd);
+			return (-1);
+		}
+	}
+
+	return (fd);
+}
+
+static void
+fileargs_set_cache(fileargs_t *fa, nvlist_t *nvl)
+{
+
+	nvlist_destroy(fa->fa_cache);
+	fa->fa_cache = nvl;
+}
+
+static nvlist_t*
+fileargs_fetch(fileargs_t *fa, const char *name)
+{
+	nvlist_t *nvl;
+	int serrno;
+
+	assert(fa != NULL);
+	assert(name != NULL);
+
+	nvl = nvlist_create(NV_FLAG_NO_UNIQUE);
+	nvlist_add_string(nvl, "cmd", "open");
+	nvlist_add_string(nvl, "name", name);
+
+	nvl = cap_xfer_nvlist(fa->fa_chann, nvl);
+	if (nvl == NULL)
+		return (NULL);
+
+	if (nvlist_get_number(nvl, "error") != 0) {
+		serrno = (int)nvlist_get_number(nvl, "error");
+		nvlist_destroy(nvl);
+		errno = serrno;
+		return (NULL);
+	}
+
+	return (nvl);
+}
+
+static nvlist_t *
+fileargs_create_limit(int argc, const char * const *argv, int flags,
+    mode_t mode, cap_rights_t *rightsp)
+{
+	nvlist_t *limits;
+	int i;
+
+	limits = nvlist_create(NV_FLAG_NO_UNIQUE);
+	if (limits == NULL)
+		return (NULL);
+
+	nvlist_add_number(limits, "flags", flags);
+	if (rightsp != NULL) {
+		nvlist_add_binary(limits, "cap_rights", rightsp,
+		    sizeof(*rightsp));
+	}
+	if ((flags & O_CREAT) != 0)
+		nvlist_add_number(limits, "mode", (uint64_t)mode);
+
+	for (i = 0; i < argc; i++) {
+		nvlist_add_null(limits, argv[i]);
+	}
+
+	return (limits);
+}
+
+static fileargs_t *
+fileargs_create(cap_channel_t *chan, int fdflags)
+{
+	fileargs_t *fa;
+
+	fa = malloc(sizeof(*fa));
+	if (fa != NULL) {
+		fa->fa_cache = NULL;
+		fa->fa_chann = chan;
+		fa->fa_fdflags = fdflags;
+		fa->fa_magic = FILEARGS_MAGIC;
+	}
+
+	return (fa);
+}
+
+fileargs_t *
+fileargs_init(int argc, char *argv[], int flags, mode_t mode,
+    cap_rights_t *rightsp)
+{
+	nvlist_t *limits;
+
+	if (argv <= 0 || argv == NULL) {
+		return (fileargs_create(NULL, 0));
+	}
+
+	limits = fileargs_create_limit(argc, (const char * const *)argv, flags,
+	   mode, rightsp);
+	if (limits == NULL)
+		return (NULL);
+
+	return (fileargs_initnv(limits));
+}
+
+fileargs_t *
+fileargs_cinit(cap_channel_t *cas, int argc, char *argv[], int flags,
+     mode_t mode, cap_rights_t *rightsp)
+{
+	nvlist_t *limits;
+
+	if (argv <= 0 || argv == NULL) {
+		return (fileargs_create(NULL, 0));
+	}
+
+	limits = fileargs_create_limit(argc, (const char * const *)argv, flags,
+	   mode, rightsp);
+	if (limits == NULL)
+		return (NULL);
+
+	return (fileargs_cinitnv(cas, limits));
+}
+
+fileargs_t *
+fileargs_initnv(nvlist_t *limits)
+{
+        cap_channel_t *cas;
+	fileargs_t *fa;
+
+	if (limits == NULL) {
+		return (fileargs_create(NULL, 0));
+	}
+
+        cas = cap_init();
+        if (cas == NULL) {
+		nvlist_destroy(limits);
+                return (NULL);
+	}
+
+        fa = fileargs_cinitnv(cas, limits);
+        cap_close(cas);
+
+	return (fa);
+}
+
+fileargs_t *
+fileargs_cinitnv(cap_channel_t *cas, nvlist_t *limits)
+{
+	cap_channel_t *chann;
+	fileargs_t *fa;
+	int serrno, ret;
+	int flags;
+
+	assert(cas != NULL);
+
+	if (limits == NULL) {
+		return (fileargs_create(NULL, 0));
+	}
+
+	chann = NULL;
+	fa = NULL;
+
+	chann = cap_service_open(cas, "system.fileargs");
+	if (chann == NULL) {
+		nvlist_destroy(limits);
+		return (NULL);
+	}
+
+	flags = nvlist_get_number(limits, "flags");
+
+	/* Limits are consumed no need to free them. */
+	ret = cap_limit_set(chann, limits);
+	if (ret < 0)
+		goto out;
+
+	fa = fileargs_create(chann, flags);
+	if (fa == NULL)
+		goto out;
+
+	return (fa);
+out:
+	serrno = errno;
+	if (chann != NULL)
+		cap_close(chann);
+	errno = serrno;
+	return (NULL);
+}
+
+int
+fileargs_open(fileargs_t *fa, const char *name)
+{
+	int fd;
+	nvlist_t *nvl;
+	char *cmd;
+
+	assert(fa != NULL);
+	assert(fa->fa_magic == FILEARGS_MAGIC);
+
+	if (name == NULL) {
+		errno = EINVAL;
+		return (-1);
+	}
+
+	if (fa->fa_chann == NULL) {
+		errno = ENOTCAPABLE;
+		return (-1);
+	}
+
+	fd = fileargs_get_cache(fa, name);
+	if (fd != -1)
+		return (fd);
+
+	nvl = fileargs_fetch(fa, name);
+	if (nvl == NULL)
+		return (-1);
+
+	fd = nvlist_take_descriptor(nvl, "fd");
+	cmd = nvlist_take_string(nvl, "cmd");
+	if (strcmp(cmd, "cache") == 0)
+		fileargs_set_cache(fa, nvl);
+	else
+		nvlist_destroy(nvl);
+	free(cmd);
+
+	return (fd);
+}
+
+FILE *
+fileargs_fopen(fileargs_t *fa, const char *name, const char *mode)
+{
+	int fd;
+
+	if ((fd = fileargs_open(fa, name)) < 0) {
+		return (NULL);
+	}
+
+	return (fdopen(fd, mode));
+}
+
+void
+fileargs_free(fileargs_t *fa)
+{
+
+	if (fa == NULL)
+		return;
+
+	assert(fa->fa_magic == FILEARGS_MAGIC);
+
+	nvlist_destroy(fa->fa_cache);
+	if (fa->fa_chann != NULL) {
+		cap_close(fa->fa_chann);
+	}
+	explicit_bzero(&fa->fa_magic, sizeof(fa->fa_magic));
+	free(fa);
+}
+
+/*
+ * Service functions.
+ */
+
+static const char *lastname;
+static void *cacheposition;
+static bool allcached;
+static const cap_rights_t *caprightsp;
+static int capflags;
+static mode_t capmode;
+
+static int
+open_file(const char *name)
+{
+	int fd, serrno;
+
+	if ((capflags & O_CREAT) == 0)
+		fd = open(name, capflags);
+	else
+		fd = open(name, capflags, capmode);
+	if (fd < 0)
+		return (-1);
+
+	if (caprightsp != NULL) {
+		if (cap_rights_limit(fd, caprightsp) < 0) {
+			serrno = errno;
+			close(fd);
+			errno = serrno;
+			return (-1);
+		}
+	}
+
+	return (fd);
+}
+
+static void
+fileargs_add_cache(nvlist_t *nvlout, const nvlist_t *limits,
+    const char *curent_name)
+{
+	int type, i, fd;
+	void *cookie;
+	nvlist_t *new;
+	const char *fname;
+
+	if ((capflags & O_CREAT) != 0) {
+		allcached = true;
+		return;
+	}
+
+	cookie = cacheposition;
+	for (i = 0; i < CACHE_SIZE + 1; i++) {
+		fname = nvlist_next(limits, &type, &cookie);
+		if (fname == NULL) {
+			cacheposition = NULL;
+			lastname = NULL;
+			allcached = true;
+			return;
+		}
+		/* We doing that to catch next element name. */
+		if (i == CACHE_SIZE) {
+			break;
+		}
+
+		if (type != NV_TYPE_NULL ||
+		    (curent_name != NULL && strcmp(fname, curent_name) == 0)) {
+			curent_name = NULL;
+			i--;
+			continue;
+		}
+
+		fd = open_file(fname);
+		if (fd < 0) {
+			i--;
+			continue;
+		}
+
+		new = nvlist_create(NV_FLAG_NO_UNIQUE);
+		nvlist_move_descriptor(new, "fd", fd);
+		nvlist_add_nvlist(nvlout, fname, new);
+	}
+	cacheposition = cookie;
+	lastname = fname;
+}
+
+static bool
+fileargs_allowed(const nvlist_t *limits, const nvlist_t *request)
+{
+	const char *name;
+
+	name = dnvlist_get_string(request, "name", NULL);
+	if (name == NULL)
+		return (false);
+
+	/* Fast path. */
+	if (lastname != NULL && strcmp(name, lastname) == 0)
+		return (true);
+
+	if (!nvlist_exists_null(limits, name))
+		return (false);
+
+	return (true);
+}
+
+static int
+fileargs_limit(const nvlist_t *oldlimits, const nvlist_t *newlimits)
+{
+
+	if (oldlimits != NULL)
+		return (ENOTCAPABLE);
+
+	capflags = (int)dnvlist_get_number(newlimits, "flags", 0);
+	if ((capflags & O_CREAT) != 0)
+		capmode = (mode_t)nvlist_get_number(newlimits, "mode");
+	else
+		capmode = 0;
+
+	caprightsp = dnvlist_get_binary(newlimits, "cap_rights", NULL, NULL, 0);
+
+	return (0);
+}
+
+static int
+fileargs_command_open(const nvlist_t *limits, nvlist_t *nvlin,
+    nvlist_t *nvlout)
+{
+	int fd;
+	const char *name;
+
+	if (limits == NULL)
+		return (ENOTCAPABLE);
+
+	if (!fileargs_allowed(limits, nvlin))
+		return (ENOTCAPABLE);
+
+	name = nvlist_get_string(nvlin, "name");
+
+	fd = open_file(name);
+	if (fd < 0)
+		return (errno);
+
+	if (!allcached && (lastname == NULL ||
+	    strcmp(name, lastname) == 0)) {
+		nvlist_add_string(nvlout, "cmd", "cache");
+		fileargs_add_cache(nvlout, limits, name);
+	} else {
+		nvlist_add_string(nvlout, "cmd", "open");
+	}
+	nvlist_move_descriptor(nvlout, "fd", fd);
+	return (0);
+}
+
+static int
+fileargs_command(const char *cmd, const nvlist_t *limits,
+    nvlist_t *nvlin, nvlist_t *nvlout)
+{
+
+	if (strcmp(cmd, "open") == 0)
+		return (fileargs_command_open(limits, nvlin, nvlout));
+
+	return (EINVAL);
+}
+
+CREATE_SERVICE("system.fileargs", fileargs_limit, fileargs_command,
+    CASPER_SERVICE_FD | CASPER_SERVICE_STDIO | CASPER_SERVICE_NO_UNIQ_LIMITS);

lib/libcasper/services/cap_fileargs/cap_fileargs.h

@@ -0,0 +1,108 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
+ * All rights reserved.
+ *
+ * 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 AUTHORS 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 AUTHORS 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.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _FILEARGS_H_
+#define	_FILEARGS_H_
+
+#include <sys/dnv.h>
+#include <sys/nv.h>
+
+#include <stdbool.h>
+
+#ifdef WITH_CASPER
+struct fileargs;
+typedef struct fileargs fileargs_t;
+
+fileargs_t *fileargs_init(int argc, char *argv[], int flags, mode_t mode,
+    cap_rights_t *rightsp);
+fileargs_t *fileargs_cinit(cap_channel_t *cas, int argc, char *argv[],
+    int flags, mode_t mode, cap_rights_t *rightsp);
+fileargs_t *fileargs_initnv(nvlist_t *limits);
+fileargs_t *fileargs_cinitnv(cap_channel_t *cas, nvlist_t *limits);
+int fileargs_open(fileargs_t *fa, const char *name);
+void fileargs_free(fileargs_t *fa);
+FILE *fileargs_fopen(fileargs_t *fa, const char *name, const char *mode);
+#else
+typedef struct fileargs {
+	int	fa_flags;
+	mode_t	fa_mode;
+} fileargs_t;
+
+static inline fileargs_t *
+fileargs_init(int argc __unused, char *argv[] __unused, int flags, mode_t mode,
+    cap_rights_t *rightsp __unused) {
+	fileargs_t *fa;
+
+	fa = malloc(sizeof(*fa));
+	if (fa != NULL) {
+		fa->fa_flags = flags;
+		fa->fa_mode = mode;
+	}
+
+	return (fa);
+}
+
+static inline fileargs_t *
+fileargs_cinit(cap_channel_t *cas __unused, int argc, char *argv[], int flags,
+    mode_t mode, cap_rights_t *rightsp)
+{
+
+	return (fileargs_init(argc, argv, flags, mode, rightsp));
+}
+
+static inline fileargs_t *
+fileargs_initnv(nvlist_t *limits)
+{
+	fileargs_t *fa;
+
+	fa = fileargs_init(0, NULL,
+	    nvlist_get_number(limits, "flags"),
+	    dnvlist_get_number(limits, "mode", 0),
+	    NULL);
+	nvlist_destroy(limits);
+
+	return (fa);
+}
+
+static inline fileargs_t *
+fileargs_cinitnv(cap_channel_t *cas __unused, nvlist_t *limits)
+{
+
+	return (fileargs_initnv(limits));
+}
+
+#define	fileargs_open(fa, name)							\
+	open(name, fa->fa_flags, fa->fa_mode)
+#define	fileargs_fopen(fa, name, mode)						\
+	fopen(name, mode)
+#define	fileargs_free(fa)	(free(fa))
+#endif
+
+#endif	/* !_FILEARGS_H_ */

share/mk/src.libnames.mk

@@ -75,6 +75,7 @@ _LIBRARIES=	\
 		cam \
 		casper \
 		cap_dns \
+		cap_fileargs \
 		cap_grp \
 		cap_pwd \
 		cap_random \
@@ -238,6 +239,7 @@ _DP_cam=	sbuf
 _DP_kvm=	elf
 _DP_casper=	nv
 _DP_cap_dns=	nv
+_DP_cap_fileargs=	nv
 _DP_cap_grp=	nv
 _DP_cap_pwd=	nv
 _DP_cap_random=	nv