On Sun, Nov 18, 2018 at 9:13 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > On Sun, Nov 18, 2018 at 8:29 AM Daniel Colascione <dancol@xxxxxxxxxx> wrote: >> >> On Sun, Nov 18, 2018 at 8:17 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: >> > On Sun, Nov 18, 2018 at 7:53 AM Daniel Colascione <dancol@xxxxxxxxxx> wrote: >> >> >> >> On Sun, Nov 18, 2018 at 7:38 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: >> >> > I fully agree that a more comprehensive, less expensive API for >> >> > managing processes would be nice. But I also think that this patch >> >> > (using the directory fd and ioctl) is better from a security >> >> > perspective than using a new file in /proc. >> >> >> >> That's an assertion, not an argument. And I'm not opposed to an >> >> operation on the directory FD, now that it's clear Linus has banned >> >> "write(2)-as-a-command" APIs. I just insist that we implement the API >> >> with a system call instead of a less-reliable ioctl due to the >> >> inherent namespace collision issues in ioctl command names. >> > >> > Linus banned it because of bugs iike the ones in the patch. >> >> Maybe: he didn't provide a reason. What's your point? > > My point is that an API that involves a file like /proc/PID/kill is > very tricky to get right. Here are some considerations: Moot. write(2) for this interface is off the table anyway. The right approach here is a system call that accepts a /proc/pid directory file descriptor, a signal number, and a signal information field (as in sigqueue(2)). > Now if we had an ioctlat() API, maybe it would make sense. But we > don't, and I think it would be a bit crazy to add one. A process is not a driver. Why won't this idea of using an ioctl for the kill-process-by-dfd thing just won't die? An ioctl has *zero* advantage in this context.
