Author: jonathan
Date: Fri Jun 20 17:08:32 2014
New Revision: 267678
URL: http://svnweb.freebsd.org/changeset/base/267678
Log:
Add the LD_LIBRARY_PATH_FDS environmental variable.
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
Modified:
head/libexec/rtld-elf/rtld.1
head/libexec/rtld-elf/rtld.c
head/libexec/rtld-elf/rtld_printf.c
head/libexec/rtld-elf/rtld_printf.h
Modified: head/libexec/rtld-elf/rtld.1
==============================================================================
--- head/libexec/rtld-elf/rtld.1 Fri Jun 20 15:43:58 2014
(r267677)
+++ head/libexec/rtld-elf/rtld.1 Fri Jun 20 17:08:32 2014
(r267678)
@@ -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
.Sh SEE ALSO
.Xr ld 1 ,
.Xr ldd 1 ,
+.Xr capsicum 4 ,
.Xr elf 5 ,
.Xr libmap.conf 5 ,
.Xr ldconfig 8
Modified: head/libexec/rtld-elf/rtld.c
==============================================================================
--- head/libexec/rtld-elf/rtld.c Fri Jun 20 15:43:58 2014
(r267677)
+++ head/libexec/rtld-elf/rtld.c Fri Jun 20 17:08:32 2014
(r267678)
@@ -94,7 +94,7 @@ static bool donelist_check(DoneList *, c
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 *,
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 *
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
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_
*/
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_
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 Ob
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 Ob
(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,
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, co
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, cons
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.
*/
Modified: head/libexec/rtld-elf/rtld_printf.c
==============================================================================
--- head/libexec/rtld-elf/rtld_printf.c Fri Jun 20 15:43:58 2014
(r267677)
+++ head/libexec/rtld-elf/rtld_printf.c Fri Jun 20 17:08:32 2014
(r267678)
@@ -429,6 +429,18 @@ number:
}
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)
{
struct snprintf_arg info;
Modified: head/libexec/rtld-elf/rtld_printf.h
==============================================================================
--- head/libexec/rtld-elf/rtld_printf.h Fri Jun 20 15:43:58 2014
(r267677)
+++ head/libexec/rtld-elf/rtld_printf.h Fri Jun 20 17:08:32 2014
(r267678)
@@ -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);
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