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Add the LD_LIBRARY_PATH_FDS environmental variable.

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This variable allows the loading of shared libraries via directory descriptors
rather than via library paths.  If LD_LIBRARY_PATH_FDS=3:4:12, the directories
represented by file descriptors 3, 4 and 12 will searched for shared libraries
before the normal path-based mechanisms are used.  This allows us to execute
unprivileged binaries from within a Capsicum sandbox even if they require
shared libraries.

Approved by:	rwatson (mentor)
Reviewed by:	kib
MFC after:	3 weeks
Sponsored by:	DARPA/AFRL
This commit is contained in:
Jonathan Anderson 2014-06-20 17:08:32 +00:00
parent eb0fb866de
commit 02d3b38e0a
4 changed files with 148 additions and 16 deletions
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10
libexec/rtld-elf/rtld.1
View File

@ -28,7 +28,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd June 28, 2012
.Dd June 20, 2014
.Dt RTLD 1
.Os
.Sh NAME
@ -192,6 +192,13 @@ the directories specified by
will be searched first
followed by the set of built-in standard directories.
This variable is unset for set-user-ID and set-group-ID programs.
.Ev LD_LIBRARY_PATH_FDS
A colon separated list of file descriptor numbers for library directories.
This is intended for use within
.Xr capsicum 4
sandboxes, when global namespaces such as the filesystem are unavailable.
It is consulted just after LD_LIBRARY_PATH.
This variable is unset for set-user-ID and set-group-ID programs.
.It Ev LD_BIND_NOW
When set to a nonempty string, causes
.Nm
@ -283,6 +290,7 @@ The libmap configuration file for 32-bit binaries on 64-bit system.
.Sh SEE ALSO
.Xr ld 1 ,
.Xr ldd 1 ,
.Xr capsicum 4 ,
.Xr elf 5 ,
.Xr libmap.conf 5 ,
.Xr ldconfig 8

140
libexec/rtld-elf/rtld.c
View File

@ -94,7 +94,7 @@ static bool donelist_check(DoneList *, const Obj_Entry *);
static void errmsg_restore(char *);
static char *errmsg_save(void);
static void *fill_search_info(const char *, size_t, void *);
static char *find_library(const char *, const Obj_Entry *);
static char *find_library(const char *, const Obj_Entry *, int *);
static const char *gethints(bool);
static void init_dag(Obj_Entry *);
static void init_pagesizes(Elf_Auxinfo **aux_info);
@ -119,6 +119,7 @@ static void objlist_push_head(Objlist *, Obj_Entry *);
static void objlist_push_tail(Objlist *, Obj_Entry *);
static void objlist_put_after(Objlist *, Obj_Entry *, Obj_Entry *);
static void objlist_remove(Objlist *, Obj_Entry *);
static int parse_libdir(const char *);
static void *path_enumerate(const char *, path_enum_proc, void *);
static int relocate_object_dag(Obj_Entry *root, bool bind_now,
Obj_Entry *rtldobj, int flags, RtldLockState *lockstate);
@ -133,6 +134,7 @@ static int rtld_dirname_abs(const char *, char *);
static void *rtld_dlopen(const char *name, int fd, int mode);
static void rtld_exit(void);
static char *search_library_path(const char *, const char *);
static char *search_library_pathfds(const char *, const char *, int *);
static const void **get_program_var_addr(const char *, RtldLockState *);
static void set_program_var(const char *, const void *);
static int symlook_default(SymLook *, const Obj_Entry *refobj);
@ -178,6 +180,7 @@ static bool dangerous_ld_env; /* True if environment variables have been
static char *ld_bind_now; /* Environment variable for immediate binding */
static char *ld_debug; /* Environment variable for debugging */
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_elf_hints_path; /* Environment variable for alternative hints path */
@ -401,7 +404,8 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
*/
if (!trust) {
if (unsetenv(LD_ "PRELOAD") || unsetenv(LD_ "LIBMAP") ||
unsetenv(LD_ "LIBRARY_PATH") || unsetenv(LD_ "LIBMAP_DISABLE") ||
unsetenv(LD_ "LIBRARY_PATH") || unsetenv(LD_ "LIBRARY_PATH_FDS") ||
unsetenv(LD_ "LIBMAP_DISABLE") ||
unsetenv(LD_ "DEBUG") || unsetenv(LD_ "ELF_HINTS_PATH") ||
unsetenv(LD_ "LOADFLTR") || unsetenv(LD_ "LIBRARY_PATH_RPATH")) {
_rtld_error("environment corrupt; aborting");
@ -412,6 +416,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
libmap_disable = getenv(LD_ "LIBMAP_DISABLE") != NULL;
libmap_override = getenv(LD_ "LIBMAP");
ld_library_path = getenv(LD_ "LIBRARY_PATH");
ld_library_dirs = getenv(LD_ "LIBRARY_PATH_FDS");
ld_preload = getenv(LD_ "PRELOAD");
ld_elf_hints_path = getenv(LD_ "ELF_HINTS_PATH");
ld_loadfltr = getenv(LD_ "LOADFLTR") != NULL;
@ -1417,6 +1422,7 @@ gnu_hash(const char *s)
return (h & 0xffffffff);
}
/*
* Find the library with the given name, and return its full pathname.
* The returned string is dynamically allocated. Generates an error
@ -1425,6 +1431,10 @@ gnu_hash(const char *s)
* If the second argument is non-NULL, then it refers to an already-
* loaded shared object, whose library search path will be searched.
*
* If a library is successfully located via LD_LIBRARY_PATH_FDS, its
* descriptor (which is close-on-exec) will be passed out via the third
* argument.
*
* The search order is:
* DT_RPATH in the referencing file _unless_ DT_RUNPATH is present (1)
* DT_RPATH of the main object if DSO without defined DT_RUNPATH (1)
@ -1437,7 +1447,7 @@ gnu_hash(const char *s)
* (1) Handled in digest_dynamic2 - rpath left NULL if runpath defined.
*/
static char *
find_library(const char *xname, const Obj_Entry *refobj)
find_library(const char *xname, const Obj_Entry *refobj, int *fdp)
{
char *pathname;
char *name;
@ -1474,6 +1484,7 @@ find_library(const char *xname, const Obj_Entry *refobj)
if ((pathname = search_library_path(name, ld_library_path)) != NULL ||
(refobj != NULL &&
(pathname = search_library_path(name, refobj->rpath)) != NULL) ||
(pathname = search_library_pathfds(name, ld_library_dirs, fdp)) != NULL ||
(pathname = search_library_path(name, gethints(false))) != NULL ||
(pathname = search_library_path(name, STANDARD_LIBRARY_PATH)) != NULL)
return (pathname);
@ -1486,6 +1497,7 @@ find_library(const char *xname, const Obj_Entry *refobj)
(pathname = search_library_path(name, ld_library_path)) != NULL ||
(objgiven &&
(pathname = search_library_path(name, refobj->runpath)) != NULL) ||
(pathname = search_library_pathfds(name, ld_library_dirs, fdp)) != NULL ||
(pathname = search_library_path(name, gethints(nodeflib))) != NULL ||
(objgiven && !nodeflib &&
(pathname = search_library_path(name, STANDARD_LIBRARY_PATH)) != NULL))
@ -2085,29 +2097,34 @@ load_object(const char *name, int fd_u, const Obj_Entry *refobj, int flags)
struct stat sb;
char *path;
fd = -1;
if (name != NULL) {
for (obj = obj_list->next; obj != NULL; obj = obj->next) {
if (object_match_name(obj, name))
return (obj);
}
path = find_library(name, refobj);
path = find_library(name, refobj, &fd);
if (path == NULL)
return (NULL);
} else
path = NULL;
/*
* If we didn't find a match by pathname, or the name is not
* supplied, open the file and check again by device and inode.
* This avoids false mismatches caused by multiple links or ".."
* in pathnames.
*
* To avoid a race, we open the file and use fstat() rather than
* using stat().
*/
fd = -1;
if (fd_u == -1) {
if (fd >= 0) {
/*
* search_library_pathfds() opens a fresh file descriptor for the
* library, so there is no need to dup().
*/
} else if (fd_u == -1) {
/*
* If we didn't find a match by pathname, or the name is not
* supplied, open the file and check again by device and inode.
* This avoids false mismatches caused by multiple links or ".."
* in pathnames.
*
* To avoid a race, we open the file and use fstat() rather than
* using stat().
*/
if ((fd = open(path, O_RDONLY | O_CLOEXEC)) == -1) {
_rtld_error("Cannot open \"%s\"", path);
free(path);
@ -2745,6 +2762,69 @@ search_library_path(const char *name, const char *path)
return (p);
}
/*
* Finds the library with the given name using the directory descriptors
* listed in the LD_LIBRARY_PATH_FDS environment variable.
*
* Returns a freshly-opened close-on-exec file descriptor for the library,
* or -1 if the library cannot be found.
*/
static char *
search_library_pathfds(const char *name, const char *path, int *fdp)
{
char *envcopy, *fdstr, *found, *last_token;
size_t len;
int dirfd, fd;
dbg("%s('%s', '%s', fdp)\n", __func__, name, path);
/* Don't load from user-specified libdirs into setuid binaries. */
if (!trust)
return (NULL);
/* We can't do anything if LD_LIBRARY_PATH_FDS isn't set. */
if (path == NULL)
return (NULL);
/* LD_LIBRARY_PATH_FDS only works with relative paths. */
if (name[0] == '/') {
dbg("Absolute path (%s) passed to %s", name, __func__);
return (NULL);
}
/*
* Use strtok_r() to walk the FD:FD:FD list. This requires a local
* copy of the path, as strtok_r rewrites separator tokens
* with '\0'.
*/
found = NULL;
envcopy = xstrdup(path);
for (fdstr = strtok_r(envcopy, ":", &last_token); fdstr != NULL;
fdstr = strtok_r(NULL, ":", &last_token)) {
dirfd = parse_libdir(fdstr);
if (dirfd < 0)
break;
fd = openat(dirfd, name, O_RDONLY | O_CLOEXEC);
if (fd >= 0) {
*fdp = fd;
len = strlen(fdstr) + strlen(name) + 3;
found = xmalloc(len);
if (rtld_snprintf(found, len, "#%d/%s", dirfd, name) < 0) {
_rtld_error("error generating '%d/%s'",
dirfd, name);
die();
}
dbg("open('%s') => %d", found, fd);
break;
}
}
free(envcopy);
return (found);
}
int
dlclose(void *handle)
{
@ -4835,6 +4915,36 @@ symlook_init_from_req(SymLook *dst, const SymLook *src)
dst->lockstate = src->lockstate;
}
/*
* Parse a file descriptor number without pulling in more of libc (e.g. atoi).
*/
static int
parse_libdir(const char *str)
{
static const int RADIX = 10; /* XXXJA: possibly support hex? */
const char *orig;
int fd;
char c;
orig = str;
fd = 0;
for (c = *str; c != '\0'; c = *++str) {
if (c < '0' || c > '9')
return (-1);
fd *= RADIX;
fd += c - '0';
}
/* Make sure we actually parsed something. */
if (str == orig) {
_rtld_error("failed to parse directory FD from '%s'", str);
return (-1);
}
return (fd);
}
/*
* Overrides for libc_pic-provided functions.
*/

12
libexec/rtld-elf/rtld_printf.c
View File

@ -428,6 +428,18 @@ reswitch: switch (ch = (u_char)*fmt++) {
#undef PCHAR
}
int
rtld_snprintf(char *buf, size_t bufsize, const char *fmt, ...)
{
va_list ap;
int retval;
va_start(ap, fmt);
retval = rtld_vsnprintf(buf, bufsize, fmt, ap);
va_end(ap);
return (retval);
}
int
rtld_vsnprintf(char *buf, size_t bufsize, const char *fmt, va_list ap)
{

2
libexec/rtld-elf/rtld_printf.h
View File

@ -31,6 +31,8 @@
#include <sys/cdefs.h>
#include <unistd.h>
int rtld_snprintf(char *buf, size_t bufsize, const char *fmt, ...)
__printflike(3, 4);
int rtld_vsnprintf(char *buf, size_t bufsize, const char *fmt, va_list ap);
int rtld_vfdprintf(int fd, const char *fmt, va_list ap);
int rtld_fdprintf(int fd, const char *fmt, ...) __printflike(2, 3);