Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 25 Mar 2019 16:42:14 -0700 | Subject | Re: pidfd design |
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On Mon, Mar 25, 2019 at 1:23 PM Daniel Colascione <dancol@google.com> wrote: > > On Mon, Mar 25, 2019 at 1:14 PM Jann Horn <jannh@google.com> wrote: > > > > On Mon, Mar 25, 2019 at 8:44 PM Andy Lutomirski <luto@kernel.org> wrote:
> > One ioctl on procfs roots to translate pidfds into that procfs, > > subject to both the normal lookup permission checks and only working > > if the pidfd has a translation into the procfs: > > > > int proc_root_fd = open("/proc", O_RDONLY); > > int proc_dir_fd = ioctl(proc_root_fd, PROC_PIDFD_TO_PROCFSFD, pidfd); > > > > And one ioctl on procfs directories to translate from PGIDs and PIDs to pidfds: > > > > int proc_pgid_fd = open("/proc/self", O_RDONLY); > > int self_pg_pidfd = ioctl(proc_pgid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > > int proc_pid_fd = open("/proc/thread-self", O_RDONLY); > > int self_p_pidfd = ioctl(proc_pid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > >
This sounds okay to me. Or we could make it so that a procfs directory fd also works as a pidfd, but that seems more likely to be problematic than just allowing two-way translation like this
> > > > And then, as you proposed, the new sys_clone() can just return a > > pidfd, and you can convert it into a procfs fd yourself if you want. > > I think that's the consensus we reached on the other thread. The > O_DIRECTORY open on /proc/self/fd/mypidfd seems like it'd work well > enough.
I must have missed this particular email.
IMO, if /proc/self/fd/mypidfd allows O_DIRECTORY open to work, then it really ought to do function just like /proc/self/fd/mypidfd/. and /proc/self/fd/mypidfd/status should work. And these latter two options seem nutty.
Also, this O_DIRECTORY thing is missing the entire point of the ioctl interface -- it doesn't require procfs access.
--Andy
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