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|
#include "substitute.h"
#include "substitute-internal.h"
#include <mach/mach.h>
#include <mach-o/dyld.h>
#include <spawn.h>
#include <sys/wait.h>
#include <syslog.h>
#include <malloc/malloc.h>
extern char ***_NSGetEnviron(void);
static __typeof__(posix_spawn) *old_posix_spawn, *old_posix_spawnp,
hook_posix_spawn, hook_posix_spawnp;
static __typeof__(wait4) *old_wait4, hook_wait4;
static __typeof__(waitpid) *old_waitpid, hook_waitpid;
static bool advance(char **strp, const char *template) {
size_t len = strlen(template);
if (!strncmp(*strp, template, len)) {
*strp += len;
return true;
}
return false;
}
static int hook_posix_spawn_generic(__typeof__(posix_spawn) *old,
pid_t *restrict pid, const char *restrict path,
const posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *restrict attrp,
char *const argv[restrict],
char *const envp[restrict]) {
char *new = NULL;
char **new_envp = NULL;
char *const *envp_to_use = envp;
char *const *my_envp = envp ? envp : *_NSGetEnviron();
posix_spawnattr_t my_attr = NULL;
/* This mirrors Substrate's logic with safe mode. I don't really
* understand the point of the difference between its 'safe' (which removes
* Substrate from DYLD_INSERT_LIBRARIES) and 'quit' (which just skips
* directly to the original spawn), but I guess I'll just do the same for
* maximum safety... */
bool safe_mode = false;
const char *orig_dyld_insert = "";
static const char my_dylib[] =
"/Library/Substitute/generic-dyld-inserted.dylib";
size_t env_count = 0;
for (char *const *ep = my_envp; *ep; ep++) {
env_count++;
char *env = *ep;
if (advance(&env, "_MSSafeMode=") || advance(&env, "_SubstituteSafeMode=")) {
if (!strcmp(env, "0") || !strcmp(env, "NO"))
continue;
else if (!strcmp(env, "1") || !strcmp(env, "YES"))
safe_mode = true;
else
goto skip;
} else if (advance(&env, "DYLD_INSERT_LIBRARIES=")) {
orig_dyld_insert = env;
}
}
new = malloc(sizeof("DYLD_INSERT_LIBRARIES=") - 1 +
sizeof(my_dylib) - 1 +
strlen(orig_dyld_insert) + 1);
char *newp_orig = stpcpy(new, "DYLD_INSERT_LIBRARIES=");
char *newp = newp_orig;
const char *p = orig_dyld_insert;
while (*p) { /* W.N.H. */
const char *next = strchr(p, ':') ?: (p + strlen(p));
/* append if it isn't a copy of ours */
if (!(next - p == sizeof(my_dylib) - 1 &&
memcmp(next, my_dylib, sizeof(my_dylib) - 1))) {
if (newp != newp_orig)
*newp++ = ':';
memcpy(newp, p, next - p);
newp += next - p;
}
}
/* append ours if necessary */
if (!safe_mode) {
if (newp != newp_orig)
*newp++ = ':';
newp = stpcpy(newp, my_dylib);
}
/* no libraries? then just get rid of it */
if (newp == newp_orig) {
free(new);
new = NULL;
}
new_envp = malloc(sizeof(char *) * (env_count + 2));
envp_to_use = new_envp;
char **outp = new_envp;
for (size_t idx = 0; idx < env_count; idx++) {
char *env = envp[idx];
/* remove *all* D_I_L, including duplicates */
if (!advance(&env, "DYLD_INSERT_LIBRARIES="))
*outp++ = env;
}
if (new)
*outp++ = new;
*outp++ = NULL;
if (safe_mode)
goto skip;
/* Deal with the dumb __restrict section. A complication is that this
* could actually be an exec. */
if (attrp) {
posix_spawnattr_t attr = *attrp;
size_t size = malloc_size(attr);
my_attr = malloc(size);
if (!my_attr)
goto crap;
memcpy(my_attr, attr, size);
} else {
if (posix_spawnattr_init(&my_attr))
goto crap;
}
short flags;
if (posix_spawnattr_getflags(&my_attr, &flags))
goto crap;
bool was_suspended = flags & POSIX_SPAWN_START_SUSPENDED;
flags |= POSIX_SPAWN_START_SUSPENDED;
if (posix_spawnattr_setflags(&my_attr, flags))
goto crap;
if (flags & POSIX_SPAWN_SETEXEC) {
const char *prog = "/Library/Substitute/unrestrict-me";
char pid[32];
sprintf(pid, "%ld", (long) getpid());
const char *should_resume = was_suspended ? "0" : "1";
const char *argv[] = {prog, pid, should_resume, NULL};
pid_t prog_pid;
if (old_posix_spawn(&prog_pid, prog, NULL, NULL, (char **) argv, envp)) {
syslog(LOG_EMERG,
"posixspawn-hook: couldn't start unrestrict-me - oh well...");
goto skip;
}
}
int ret = old(pid, path, file_actions, &my_attr, argv, envp_to_use);
if (ret)
goto cleanup;
/* Since it returned, obviously it was not SETEXEC, so we need to
* unrestrict ourself. */
int sret = substitute_ios_unrestrict(*pid, !was_suspended);
if (sret) {
syslog(LOG_EMERG, "posixspawn-hook: substitute_ios_unrestrict => %d", sret);
}
goto cleanup;
crap:
syslog(LOG_EMERG, "posixspawn-hook: weird error - OOM? skipping our stuff");
skip:
ret = old(pid, path, file_actions, attrp, argv, envp);
cleanup:
free(new_envp);
free(new);
free(my_attr);
return ret;
}
static void after_wait_generic(pid_t pid, int stat) {
(void) pid;
(void) stat;
}
int hook_posix_spawn(pid_t *restrict pid, const char *restrict path,
const posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *restrict attrp,
char *const argv[restrict], char *const envp[restrict]) {
return hook_posix_spawn_generic(old_posix_spawn, pid, path, file_actions,
attrp, argv, envp);
}
int hook_posix_spawnp(pid_t *restrict pid, const char *restrict path,
const posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *restrict attrp,
char *const argv[restrict], char *const envp[restrict]) {
return hook_posix_spawn_generic(old_posix_spawnp, pid, path, file_actions,
attrp, argv, envp);
}
pid_t hook_wait4(pid_t pid, int *stat_loc, int options, struct rusage *rusage) {
pid_t ret = old_wait4(pid, stat_loc, options, rusage);
after_wait_generic(ret, *stat_loc);
return ret;
}
pid_t hook_waitpid(pid_t pid, int *stat_loc, int options) {
pid_t ret = old_waitpid(pid, stat_loc, options);
after_wait_generic(ret, *stat_loc);
return ret;
}
void substitute_init(struct shuttle *shuttle, UNUSED size_t nshuttle) {
/* Note: I'm using interposing to minimize the chance of conflict with
* Substrate. This shouldn't actually be necessary, because MSHookProcess,
* at least as of the old version I'm looking at the source code of, blocks
* until the thread it remotely creates exits, and that thread does
* pthread_join on the 'real' pthread it creates to do the dlopen (unlike
* the equivalent in Substitute - the difference is to decrease dependence
* on pthread internals). substitute_dlopen_in_pid does not, but that's
* what the notify port is for. Meanwhile, the jailbreak I have installed
* properly runs rc.d sequentially, so the injection tools won't do their
* thing at the same time. But just in case any of that doesn't hold up...
*/
struct substitute_image *im = substitute_open_image(_dyld_get_image_name(0));
if (!im) {
syslog(LOG_EMERG, "posixspawn-hook: substitute_open_image failed");
goto end;
}
static const struct substitute_import_hook hooks[] = {
{"_posix_spawn", hook_posix_spawn, &old_posix_spawn},
{"_posix_spawnp", hook_posix_spawnp, &old_posix_spawnp},
{"_waitpid", hook_waitpid, &old_waitpid},
{"_wait4", hook_wait4, &old_wait4},
};
int err = substitute_interpose_imports(im, hooks, sizeof(hooks)/sizeof(*hooks), 0);
if (err) {
syslog(LOG_EMERG, "posixspawn-hook: substitute_interpose_imports failed: %s",
substitute_strerror(err));
goto end;
}
end:
if (im)
substitute_close_image(im);
mach_port_t notify_port = shuttle[0].u.mach.port;
mach_msg_header_t done_hdr;
done_hdr.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_MOVE_SEND, 0);
done_hdr.msgh_size = sizeof(done_hdr);
done_hdr.msgh_remote_port = notify_port;
done_hdr.msgh_local_port = 0;
done_hdr.msgh_voucher_port = 0;
done_hdr.msgh_id = 42;
if (mach_msg_send(&done_hdr)) /* MOVE deallocates port */
syslog(LOG_EMERG, "posixspawn-hook: mach_msg_send failed");
}
|
