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rtld: introduce PRELOAD_FDS

Browse source 
The new PRELOAD_FDS variable accepts a list of file descriptors
that should be loaded into the process.

This may be used to optimize a loading process - in the case when
we already have a file descriptor to the library; we don't have
to look into multiple PATH to find it.

It may also be used in capability mode to load a single additional
library without the need to open a directory that contains it.

The last use of this functionality t may be a race-free method
of loading libraries.

Reviewed by:	kib, markj
Differential Revision:	https://reviews.freebsd.org/D29334
This commit is contained in:
Mariusz Zaborski 2021-03-24 22:10:33 +01:00
parent 852a88a1d9
commit f90218886f
7 changed files with 277 additions and 61 deletions
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10
libexec/rtld-elf/rtld.1
View file

@ -28,7 +28,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd June 1, 2020
.Dd March 24, 2021
.Dt RTLD 1
.Os
.Sh NAME
@ -189,6 +189,14 @@ to be linked in before any
other shared libraries.
If the directory is not specified then
the directories specified by
.It Ev LD_PRELOAD_PATH_FDS
A colon separated list of file descriptor numbers for libraries.
This is intended for preloading libraries in which we already have a file
descriptor.
This may optimize the process of loading libraries because we do not have to
look for them in directories.
It may also be useful in a capability base system where we do not have access to
global namespaces such as the filesystem.
.Ev LD_LIBRARY_PATH
will be searched first
followed by the set of built-in standard directories.

33
libexec/rtld-elf/rtld.c
View file

@ -119,7 +119,7 @@ static void linkmap_delete(Obj_Entry *);
static void load_filtees(Obj_Entry *, int flags, RtldLockState *);
static void unload_filtees(Obj_Entry *, RtldLockState *);
static int load_needed_objects(Obj_Entry *, int);
static int load_preload_objects(void);
static int load_preload_objects(char *, bool);
static Obj_Entry *load_object(const char *, int fd, const Obj_Entry *, int);
static void map_stacks_exec(RtldLockState *);
static int obj_disable_relro(Obj_Entry *);
@ -210,6 +210,8 @@ static char *ld_library_path; /* Environment variable for search path */
static char *ld_library_dirs; /* Environment variable for library descriptors */
static char *ld_preload; /* Environment variable for libraries to
load first */
static char *ld_preload_fds; /* Environment variable for libraries represented by
descriptors */
static const char *ld_elf_hints_path; /* Environment variable for alternative hints path */
static const char *ld_tracing; /* Called from ldd to print libs */
static char *ld_utrace; /* Use utrace() to log events. */
@ -564,7 +566,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
ld_bind_now = getenv(_LD("BIND_NOW"));
/*
/*
* If the process is tainted, then we un-set the dangerous environment
* variables. The process will be marked as tainted until setuid(2)
* is called. If any child process calls setuid(2) we do not want any
@ -575,7 +577,8 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
unsetenv(_LD("LIBRARY_PATH")) || unsetenv(_LD("LIBRARY_PATH_FDS")) ||
unsetenv(_LD("LIBMAP_DISABLE")) || unsetenv(_LD("BIND_NOT")) ||
unsetenv(_LD("DEBUG")) || unsetenv(_LD("ELF_HINTS_PATH")) ||
unsetenv(_LD("LOADFLTR")) || unsetenv(_LD("LIBRARY_PATH_RPATH"))) {
unsetenv(_LD("LOADFLTR")) || unsetenv(_LD("LIBRARY_PATH_RPATH")) ||
unsetenv(_LD("PRELOAD_FDS"))) {
_rtld_error("environment corrupt; aborting");
rtld_die();
}
@ -588,6 +591,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
ld_library_path = getenv(_LD("LIBRARY_PATH"));
ld_library_dirs = getenv(_LD("LIBRARY_PATH_FDS"));
ld_preload = getenv(_LD("PRELOAD"));
ld_preload_fds = getenv(_LD("PRELOAD_FDS"));
ld_elf_hints_path = getenv(_LD("ELF_HINTS_PATH"));
ld_loadfltr = getenv(_LD("LOADFLTR")) != NULL;
library_path_rpath = getenv(_LD("LIBRARY_PATH_RPATH"));
@ -702,8 +706,12 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
if (!libmap_disable)
libmap_disable = (bool)lm_init(libmap_override);
dbg("loading LD_PRELOAD_FDS libraries");
if (load_preload_objects(ld_preload_fds, true) == -1)
rtld_die();
dbg("loading LD_PRELOAD libraries");
if (load_preload_objects() == -1)
if (load_preload_objects(ld_preload, false) == -1)
rtld_die();
preload_tail = globallist_curr(TAILQ_LAST(&obj_list, obj_entry_q));
@ -2468,9 +2476,8 @@ load_needed_objects(Obj_Entry *first, int flags)
}
static int
load_preload_objects(void)
load_preload_objects(char *p, bool isfd)
{
char *p = ld_preload;
Obj_Entry *obj;
static const char delim[] = " \t:;";
@ -2479,12 +2486,24 @@ load_preload_objects(void)
p += strspn(p, delim);
while (*p != '\0') {
const char *name;
size_t len = strcspn(p, delim);
char savech;
int fd;
savech = p[len];
p[len] = '\0';
obj = load_object(p, -1, NULL, 0);
if (isfd) {
name = NULL;
fd = parse_integer(p);
if (fd == -1)
return (-1);
} else {
name = p;
fd = -1;
}
obj = load_object(name, fd, NULL, 0);
if (obj == NULL)
return (-1); /* XXX - cleanup */
obj->z_interpose = true;

7
libexec/rtld-elf/tests/Makefile
View file

@ -3,7 +3,14 @@
SUBDIR+= libpythagoras target
SUBDIR_DEPEND_target= libpythagoras
ATF_TESTS_C= ld_library_pathfds
ATF_TESTS_C+= ld_preload_fds
.for t in ${ATF_TESTS_C}
SRCS.$t= $t.c common.c
.endfor
WARNS?= 3
.include <bsd.test.mk>

81
libexec/rtld-elf/tests/common.c Normal file
View file

@ -0,0 +1,81 @@
/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
* Copyright 2014 Jonathan Anderson.
* Copyright 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 ``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 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.
*
* $FreeBSD$
*/
#include <atf-c.h>
#include <fcntl.h>
#include <stdio.h>
#include "common.h"
void
expect_success(int binary, char *senv)
{
char * const env[] = { senv, NULL };
try_to_run(binary, 0, env, "the hypotenuse of 3 and 4 is 5\n", "");
}
void
expect_missing_library(int binary, char *senv)
{
char * const env[] = { senv, NULL };
try_to_run(binary, 1, env, "",
"ld-elf.so.1: Shared object \"libpythagoras.so.0\" not found,"
" required by \"target\"\n");
}
void
try_to_run(int binary, int exit_status, char * const *env,
const char *expected_out, const char *expected_err)
{
pid_t child = atf_utils_fork();
if (child == 0) {
char * const args[] = { "target", NULL };
fexecve(binary, args, env);
atf_tc_fail("fexecve() failed");
}
atf_utils_wait(child, exit_status, expected_out, expected_err);
}
int
opendir(const char *name)
{
return open(name, O_RDONLY | O_DIRECTORY);
}
int
opendirat(int parent, const char *name)
{
return openat(parent, name, O_RDONLY | O_DIRECTORY);
}

43
libexec/rtld-elf/tests/common.h Normal file
View file

@ -0,0 +1,43 @@
/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
* Copyright 2014 Jonathan Anderson.
* Copyright 2021 Mariusz Zaborski <oshogbo@vexillium.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 ``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 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 _LD_COMMON_H_
#define _LD_COMMON_H_
#define TARGET_ELF_NAME "target"
#define TARGET_LIBRARY "libpythagoras.so.0"
void expect_success(int binary, char *senv);
void expect_missing_library(int binary, char *senv);
void try_to_run(int binary, int expected_exit_status, char * const *env,
const char *expected_out, const char *expected_err);
int opendir(const char *name);
int opendirat(int parent, const char *name);
#endif /* _LD_COMMON_H_ */

56
libexec/rtld-elf/tests/ld_library_pathfds.c
View file

@ -29,6 +29,7 @@
#include <fcntl.h>
#include <stdio.h>
#include "common.h"
struct descriptors {
int binary;
@ -38,14 +39,8 @@ struct descriptors {
int usr;
};
static void setup(struct descriptors *, const atf_tc_t *);
static void expect_success(int binary, char *pathfds);
static void expect_missing_library(int binary, char *pathfds);
static void try_to_run(int binary, int expected_exit_status,
char * const *env, const char *expected_out, const char *expected_err);
static int opendir(const char *name);
static int opendirat(int parent, const char *name);
static void setup(struct descriptors *, const atf_tc_t *);
ATF_TC_WITHOUT_HEAD(missing_library);
@ -167,55 +162,10 @@ setup(struct descriptors *dp, const atf_tc_t *tc)
dp->testdir = opendir(atf_tc_get_config_var(tc, "srcdir"));
ATF_REQUIRE(dp->testdir >= 0);
ATF_REQUIRE(
(dp->binary = openat(dp->testdir, "target", O_RDONLY)) >= 0);
(dp->binary = openat(dp->testdir, TARGET_ELF_NAME, O_RDONLY)) >= 0);
ATF_REQUIRE((dp->root = opendir("/")) >= 0);
ATF_REQUIRE((dp->etc = opendirat(dp->root, "etc")) >= 0);
ATF_REQUIRE((dp->usr = opendirat(dp->root, "usr")) >= 0);
}
static void
expect_success(int binary, char *pathfds)
{
char * const env[] = { pathfds, NULL };
try_to_run(binary, 0, env, "the hypotenuse of 3 and 4 is 5\n", "");
}
static void
expect_missing_library(int binary, char *pathfds)
{
char * const env[] = { pathfds, NULL };
try_to_run(binary, 1, env, "",
"ld-elf.so.1: Shared object \"libpythagoras.so.0\" not found,"
" required by \"target\"\n");
}
static void
try_to_run(int binary, int exit_status, char * const *env,
const char *expected_out, const char *expected_err)
{
pid_t child = atf_utils_fork();
if (child == 0) {
char * const args[] = { "target", NULL };
fexecve(binary, args, env);
atf_tc_fail("fexecve() failed");
}
atf_utils_wait(child, exit_status, expected_out, expected_err);
}
static int
opendir(const char *name)
{
return open(name, O_RDONLY | O_DIRECTORY);
}
static int
opendirat(int parent, const char *name)
{
return openat(parent, name, O_RDONLY | O_DIRECTORY);
}

108
libexec/rtld-elf/tests/ld_preload_fds.c Normal file
View file

@ -0,0 +1,108 @@
/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
* Copyright 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 ``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 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.
*
* $FreeBSD$
*/
#include <atf-c.h>
#include <fcntl.h>
#include <stdio.h>
#include "common.h"
int binaryfd;
int libraryfd;
static void
setup(const atf_tc_t *tc)
{
int testdir;
testdir = opendir(atf_tc_get_config_var(tc, "srcdir"));
ATF_REQUIRE(testdir >= 0);
binaryfd = openat(testdir, TARGET_ELF_NAME, O_RDONLY);
ATF_REQUIRE(binaryfd >= 0);
libraryfd = openat(testdir, TARGET_LIBRARY, O_RDONLY);
ATF_REQUIRE(libraryfd >= 0);
close(testdir);
}
ATF_TC_WITHOUT_HEAD(missing_library);
ATF_TC_BODY(missing_library, tc)
{
setup(tc);
expect_missing_library(binaryfd, NULL);
}
ATF_TC_WITHOUT_HEAD(bad_librarys);
ATF_TC_BODY(bad_librarys, tc)
{
char *senv;
ATF_REQUIRE(asprintf(&senv, "LD_PRELOAD_FDS=::") > 0);
setup(tc);
expect_missing_library(binaryfd, senv);
}
ATF_TC_WITHOUT_HEAD(single_library);
ATF_TC_BODY(single_library, tc)
{
char *senv;
setup(tc);
ATF_REQUIRE(
asprintf(&senv, "LD_PRELOAD_FDS=%d", libraryfd) > 0);
expect_success(binaryfd, senv);
}
ATF_TC_WITHOUT_HEAD(two_librarys);
ATF_TC_BODY(two_librarys, tc)
{
char *senv;
setup(tc);
ATF_REQUIRE(
asprintf(&senv, "LD_PRELOAD_FDS=%d:%d", libraryfd, libraryfd) > 0);
expect_success(binaryfd, senv);
}
/* Register test cases with ATF. */
ATF_TP_ADD_TCS(tp)
{
ATF_TP_ADD_TC(tp, missing_library);
ATF_TP_ADD_TC(tp, bad_librarys);
ATF_TP_ADD_TC(tp, single_library);
ATF_TP_ADD_TC(tp, two_librarys);
return atf_no_error();
}