Hi Jann,
Your mail is a little cryptic. It would be best to start with
a brief summary of your point--something like the text of your
patch at the end of the mail.
On 01/06/2016 07:23 PM, Jann Horn wrote:
> Proof:
> In kernel/sys.c:
>
> case PR_SET_PDEATHSIG:
> if (!valid_signal(arg2)) {
> error = -EINVAL;
> break;
> }
> me->pdeath_signal = arg2;
> break;
I don't understand how the code above relates to the point you
want to make. (Or maybe you mean: "look, there's no check here
to see that if the parent is already dead"; but it would help
to state that explicitly).
> Testcase:
>
> #include <sys/prctl.h>
> #include <err.h>
> #include <unistd.h>
> #include <signal.h>
> #include <stdio.h>
>
> void ponk(int s) {
> puts("ponk!");
> }
>
> int main(void) {
> if (fork() == 0) {
> if (fork() == 0) {
> sleep(1);
> signal(SIGUSR1, ponk);
> prctl(PR_SET_PDEATHSIG, SIGUSR1, 0, 0, 0);
> sleep(1);
> return 0;
> }
> return 0;
> }
>
> sleep(3);
> return 0;
> }
> ---
> man2/prctl.2 | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/man2/prctl.2 b/man2/prctl.2
> index 5cea3bb..3dce8e9 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -670,6 +670,9 @@ In other words, the signal will be sent when that thread terminates
> (via, for example,
> .BR pthread_exit (3)),
> rather than after all of the threads in the parent process terminate.
> +
> +If the parent has already died by the time the parent death signal
> +is set, the new parent death signal will not be sent.
In a way, this seems almost obvious. But perhaps it is better to make the
point explicitly, as you suggest. But, because there may have been a
previous PR_SET_PDEATHSIG, I'd prefer something like this:
[[
If the caller's parent has already died by the time of this
PR_SET_PDEATHSIG operation, the operation shall have no effect.
]]
What do you think?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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