How to send a signal from a module to a process

haha · 04-22-2010, 05:19 AM

Hi,
I am writing a kernel module (2.6.31-20). I want it to send a signal to a user-space process. I have a PID of that process. The code is like this:

Code:

struct task_struct *ts;
ts = find_vpid(process_pid);
force_sig(2, ts);

I have inserted debugging printks after each line of the code. The first two lines are executed, but the last one is not and I get a "Killed" message.

Since I am a newbie to kernel module programming I would appreciate some hint of what could be wrong and what I have to do to make it work.

Thanks.

nini09 · 04-22-2010, 02:55 PM

You can use kill_proc_info function to send signal from kernel to user space.

Aquarius_Girl · 04-22-2010, 11:41 PM

Have a look at below link :
http://people.ee.ethz.ch/~arkeller/l..._howto.html#s6

archieval · 04-23-2010, 11:46 AM

You can use send_sig()

send_sig(int sig, struct task_struct *p, int priv)

akuehn · 04-26-2010, 09:39 AM

Hi!

I'm currently stuck at the same problem with kernel 2.6.32 and I followed the suggested links and here is the resulting procedure in my module.
The required process id is provided via ioctl from the associated_process.

But, I can't get the thing compiled! Actually, the find_task_by_pid_ns call is the problem. Obviously, some link is missing but which?

WARNING: "find_task_by_pid_ns" [mypath/and/modulename.ko] undefined!

static void sendSignal(void)
{
struct siginfo info;
struct task_struct *task;
int status;

/* is there a process we can send to? */
if (-1 == associated_process)
return;

task = find_task_by_pid_ns(associated_process, &init_pid_ns);
if (!task) {
printk("error finding task\n");
return;
}
info.si_signo = SIGPWR;
info.si_code = SI_QUEUE;
info.si_errno = 0; /* no recovery */

status = send_sig_info(SIGPWR, &info, task); //send the signal
if (0 > status) {
printk("error sending signal\n");
return;
}
}

Any other mistakes are not considered by now ;-)

Aquarius_Girl · 04-26-2010, 11:32 PM

Hi akuehn,

Have a look at the following link:
http://tomoyo.sourceforge.jp/cgi-bin...task_by_pid_ns

Here see the kernel version (top left) for which the function is defined
Version: linux-2.6.34

archieval · 04-27-2010, 05:49 AM

As I have said, use send_sig(), more something like this

in your kernel space driver:

struct task_struct *tsk;

your_ioctl()
{
...
case INFORM_SIG:
tsk = current;
...
}

your_send_sig_func()
{
send_sig(SIGPWR, tsk, 0);
}

Just check the signal that you want to send has the same signal number in user space, because some signal numbers are differently mapped in kernel space and user space.

Regards,
archieval

akuehn · 04-27-2010, 09:04 AM

Hi!

Thanks for the replies...

Anyway, I don't understand how to get the task_struct for my user process which has to receive the signal?
Addressing send_sig to the current task sends the signal to the module thread itself. Or do I have to walk through the whole thread structure, looking for the right pid?

Cheers
akuehn

nini09 · 04-27-2010, 02:22 PM

In the ioctl code, the "current" variable, predefined global variable in kernel space, is your user process.

your_ioctl()
{
...
case INFORM_SIG:
tsk = current;
...
}

archieval · 04-28-2010, 01:08 AM

The "current" task will be the currently executing task "at that time" when you registered or called the ioctl command before you send signal to it. You save it to a variable so that it will not refer to the "current" task that will send the signal.

Regards,
archieval

akuehn · 04-28-2010, 02:48 AM

Hey! That is it!

I didn't know that the macro "current" returns the task that is currently calling the ioctl. Thus, it is not necessary to actually provide the pid of the calling process via ioctl. It is simply the call itself.

And now it works as intended.

Thanks to all of you :-)
And have a nice day

akuehn