Re: [PATCH v1 2/2] signal: add procfd_signal() syscall

On Mon, Nov 19, 2018 at 03:39:54PM -0700, Tycho Andersen wrote:

On Mon, Nov 19, 2018 at 11:32:39AM +0100, Christian Brauner wrote:

quoted

+/**
+ *  sys_procfd_signal - send a signal to a process through a process file
+ *                      descriptor
+ *  @fd: the file descriptor of the process
+ *  @sig: signal to be sent
+ *  @info: the signal info
+ *  @flags: future flags to be passed
+ */
+SYSCALL_DEFINE4(procfd_signal, int, fd, int, sig, siginfo_t __user *, info,
+		int, flags)
+{

Can I just register an objection here that I think using a syscall
just for this is silly?

My understanding is that the concern is that some code might do:

unknown_fd = recv_fd();
ioctl(unknown_fd, SOME_IOCTL, NULL); // where SOME_IOCTL == PROC_FD_KILL
// whoops, unknown_fd was a procfd and we killed a task!

This could just be my own mental model, but for something like "kill a
task", an ioctl just seems wrong.  Syscall seems more natural.

I'd ack either method.

-serge