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Handle attaching to processes that are already session leaders.
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These are actually easier -- we just need to TIOCNOTTY, instead of
playing games with a dummy child and setsid.
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@nelhage
nelhage committed Jan 22, 2011
1 parent 84114a0 commit 065cb54
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Showing 2 changed files with 88 additions and 64 deletions.
150 changes: 87 additions & 63 deletions attach.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -94,13 +94,84 @@ void move_process_group(struct ptrace_child *child, pid_t from, pid_t to) {
closedir(dir);
}

int do_setsid(struct ptrace_child *child) {
int err = 0;
struct ptrace_child dummy;

err = ptrace_remote_syscall(child, __NR_fork,
0, 0, 0, 0, 0, 0);
if (err < 0)
return err;

debug("Forked a child: %d", child->forked_pid);

err = ptrace_finish_attach(&dummy, child->forked_pid);
if (err < 0)
goto out_kill;

dummy.state = ptrace_after_syscall;
memcpy(&dummy.user, &child->user, sizeof child->user);
if (ptrace_restore_regs(&dummy)) {
err = dummy.error;
goto out_kill;
}

err = ptrace_remote_syscall(&dummy, __NR_setpgid,
0, 0, 0, 0, 0, 0);
if (err < 0) {
error("Failed to setpgid: %s", strerror(-err));
goto out_kill;
}

move_process_group(child, child->pid, dummy.pid);

err = ptrace_remote_syscall(child, __NR_setsid,
0, 0, 0, 0, 0, 0);
if (err < 0) {
error("Failed to setsid: %s", strerror(-err));
move_process_group(child, dummy.pid, child->pid);
goto out_kill;
}

debug("Did setsid()");

out_kill:
kill(dummy.pid, SIGKILL);
ptrace_detach_child(&dummy);
ptrace_wait(&dummy);
ptrace_remote_syscall(child, __NR_waitid,
P_PID, dummy.pid, 0, WNOHANG,
0, 0);
return err;
}

int ignore_hup(struct ptrace_child *child) {
int err;
#ifdef __NR_signal
err = ptrace_remote_syscall(child, __NR_signal,
SIGHUP, (unsigned long)SIG_IGN,
0, 0, 0, 0);
#else
struct sigaction act = {
.sa_handler = SIG_IGN,
};
err = ptrace_memcpy_to_child(child, scratch_page,
&act, sizeof act);
if (err < 0)
return err;
err = ptrace_remote_syscall(child, __NR_rt_sigaction,
SIGHUP, scratch_page,
0, 8, 0, 0);
#endif
return err;
}

int attach_child(pid_t pid, const char *pty) {
struct ptrace_child child;
unsigned long scratch_page = -1;
int *child_tty_fds = NULL, n_fds, child_fd;
int i;
int err = 0;
struct ptrace_child dummy;


if (ptrace_attach_child(&child, pid))
Expand Down Expand Up @@ -162,48 +233,30 @@ int attach_child(pid_t pid, const char *pty) {

debug("Copied terminal settings");

err = ptrace_remote_syscall(&child, __NR_fork,
0, 0, 0, 0, 0, 0);
err = ignore_hup(&child);
if (err < 0)
goto out_close;

debug("Forked a child: %d", child.forked_pid);

err = ptrace_finish_attach(&dummy, child.forked_pid);
if (err < 0)
goto out_kill;

dummy.state = ptrace_after_syscall;
memcpy(&dummy.user, &child.user, sizeof child.user);
if (ptrace_restore_regs(&dummy)) {
err = dummy.error;
goto out_kill;
}

err = ptrace_remote_syscall(&dummy, __NR_setpgid,
err = ptrace_remote_syscall(&child, __NR_getsid,
0, 0, 0, 0, 0, 0);
if (err < 0) {
error("Failed to setpgid: %s", strerror(-err));
goto out_kill;
}

move_process_group(&child, child.pid, dummy.pid);

err = ptrace_remote_syscall(&child, __NR_setsid,
0, 0, 0, 0, 0, 0);
if (err < 0) {
error("Failed to setsid: %s", strerror(-err));
move_process_group(&child, dummy.pid, child.pid);
goto out_kill;
if (err != child.pid) {
debug("Target is not a session leader, attempting to setsid.");
err = do_setsid(&child);
} else {
ptrace_remote_syscall(&child, __NR_ioctl,
child_tty_fds[0], TIOCNOTTY,
0, 0, 0, 0);
}

debug("Did setsid()");
if (err < 0)
goto out_close;

err = ptrace_remote_syscall(&child, __NR_ioctl,
child_fd, TIOCSCTTY,
0, 0, 0, 0);
if (err < 0)
goto out_kill;
if (err < 0) {
error("Unable to set controlling terminal.");
goto out_close;
}

debug("Set the controlling tty");

Expand All @@ -212,38 +265,9 @@ int attach_child(pid_t pid, const char *pty) {
child_fd, child_tty_fds[i],
0, 0, 0, 0);

#ifdef __NR_signal
ptrace_remote_syscall(&child, __NR_signal,
SIGHUP, (unsigned long)SIG_IGN,
0, 0, 0, 0);
#else
{
struct sigaction act = {
.sa_handler = SIG_IGN,
};
err = ptrace_memcpy_to_child(&child, scratch_page,
&act, sizeof act);
if (err < 0)
goto out_kill;
err = ptrace_remote_syscall(&child, __NR_rt_sigaction,
SIGHUP, scratch_page,
0, 8, 0, 0);
if (err < 0)
goto out_kill;

}
#endif

err = 0;

out_kill:
kill(dummy.pid, SIGKILL);
ptrace_detach_child(&dummy);
ptrace_wait(&dummy);
ptrace_remote_syscall(&child, __NR_waitid,
P_PID, dummy.pid, 0, WNOHANG,
0, 0);

out_close:
ptrace_remote_syscall(&child, __NR_close, child_fd,
0, 0, 0, 0, 0);
Expand Down
2 changes: 1 addition & 1 deletion ptrace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,7 @@ int ptrace_wait(struct ptrace_child *child) {
ptrace_command(child, PTRACE_GETEVENTMSG, 0, &child->forked_pid);
if (child->state != ptrace_at_syscall)
child->state = ptrace_stopped;
if (sig != SIGSTOP && sig != SIGTRAP && sig != SIGCHLD) {
if (sig != SIGSTOP && sig != SIGTRAP && sig != SIGCHLD && sig != SIGHUP && sig != SIGCONT) {
child->error = EAGAIN;
return -1;
}
Expand Down

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