Messages in this thread |  | | Date | Sun, 18 Nov 2018 22:23:37 +0100 | From | Christian Brauner <> | Subject | Re: [PATCH] proc: allow killing processes via file descriptors |
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On Sun, Nov 18, 2018 at 12:54:10PM -0800, Daniel Colascione wrote: > On Sun, Nov 18, 2018 at 12:43 PM, Christian Brauner > <christian@brauner.io> wrote: > > On Sun, Nov 18, 2018 at 01:28:41PM -0700, Andy Lutomirski wrote: > >> > >> > >> > On Nov 18, 2018, at 12:44 PM, Daniel Colascione <dancol@google.com> wrote: > >> > > >> > >> > > >> > That is, I'm proposing an API that looks like this: > >> > > >> > int process_kill(int procfs_dfd, int signo, const union sigval value) > >> > > >> > If, later, process_kill were to *also* accept process-capability FDs, > >> > nothing would break. > >> > >> Except that this makes it ambiguous to the caller as to whether their current creds are considered. So it would need to be a different syscall or at least a flag. Otherwise a lot of those nice theoretical properties go away. > > > > I can add a flag argument > > int process_signal(int procfs_dfd, int signo, siginfo_t *info, int flags) > > The way I see it process_signal() should be equivalent to kill(pid, signal) for now. > > That is siginfo_t is cleared and set to: > > > > info.si_signo = sig; > > info.si_errno = 0; > > info.si_code = SI_USER; > > info.si_pid = task_tgid_vnr(current); > > info.si_uid = from_kuid_munged(current_user_ns(), current_uid()); > > That makes sense. I just don't want to get into a situation where > callers feel that they *have* to use the PID-based APIs to send a > signal because process_kill doesn't offer some bit of functionality.
Yeah.
> > Are you imagining something like requiring info t be NULL unless flags > contains some "I have a siginfo_t" value?
Well, I was actually thinking about something like:
/** * sys_process_signal - send a signal to a process trough 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(process_signal, int, fd, int, sig, siginfo_t __user *, info, int, flags) { struct pid *pid; struct fd *f; kernel_siginfo_t kinfo;
/* Do not allow users to pass garbage. */ if (flags) return -EINVAL;
int ret = __copy_siginfo_from_user(sig, &kinfo, info); if (unlikely(ret)) return ret;
/* For now, enforce that caller's creds are used. */ kinfo.si_pid = task_tgid_vnr(current); kinfo.si_uid = from_kuid_munged(current_user_ns(), current_uid());
if (signal_impersonates_kernel(kinfo)) return -EPERM;
f = fdget(fd); if (!f.file) return -EBADF;
pid = f.file->private_data; if (!pid) return -EBADF;
return kill_pid_info(sig, kinfo, pid); }
> > BTW: passing SI_USER to rt_sigqueueinfo *should* as long as the > passed-in si_pid and si_uid match what the kernel would set them to in > the kill(2) case. The whole point of SI_USER is that the recipient > knows that it can trust the origin information embedded in the > siginfo_t in the signal handler. If the kernel verifies that a signal > sender isn't actually lying, why not let people send SI_USER with > rt_sigqueueinfo?
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