On Wed, Dec 05, 2018 at 03:24:08PM -0800, Kees Cook wrote: > On Wed, Dec 5, 2018 at 12:53 PM Christian Brauner <christian@xxxxxxxxxx> wrote: > > On Wed, Dec 05, 2018 at 12:20:43PM -0600, Eric W. Biederman wrote: > > > Christian Brauner <christian@xxxxxxxxxx> writes: > > > > [1]: https://lkml.org/lkml/2018/11/18/130 > > > > [2]: https://lore.kernel.org/lkml/874lbtjvtd.fsf@xxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > [3]: https://lore.kernel.org/lkml/20181204132604.aspfupwjgjx6fhva@xxxxxxxxxx/ > > > > [4]: https://lore.kernel.org/lkml/20181203180224.fkvw4kajtbvru2ku@xxxxxxxxxx/ > > > > [5]: https://lore.kernel.org/lkml/20181121213946.GA10795@xxxxxxxxxxxxxxx/ > > > > [6]: https://lore.kernel.org/lkml/20181120103111.etlqp7zop34v6nv4@xxxxxxxxxx/ > > > > [7]: https://lore.kernel.org/lkml/36323361-90BD-41AF-AB5B-EE0D7BA02C21@xxxxxxxxxxxxxx/ > > > > [8]: https://lore.kernel.org/lkml/87tvjxp8pc.fsf@xxxxxxxxxxxx/ > > > > [9]: https://asciinema.org/a/X1J8eGhe3vCfBE2b9TXtTaSJ7 > > > > [10]: https://lore.kernel.org/lkml/20181203180224.fkvw4kajtbvru2ku@xxxxxxxxxx/ > > > > [11]: https://lore.kernel.org/lkml/F53D6D38-3521-4C20-9034-5AF447DF62FF@xxxxxxxxxxxxxx/ > > I nominate this for 2018's most-well-documented syscall commit log award. ;) Hahaha. If I win can I get my price in beer(s)? :) > > > > > + /* > > > > + * Give userspace a way to detect whether /proc/<pid>/task/<tid> fds > > > > + * are supported. > > > > + */ > > > > + ret = -EOPNOTSUPP; > > > > + if (proc_is_tid_procfd(f.file)) > > > > + goto err; > > > > > > -EBADF is the proper error code. > > > > This is done so that userspace has a way of figuring out that tid fds > > are not yet supported. This has been discussed with Florian (see commit > > message). > > Right, we should keep this -EOPNOTSUPP. > > > > > + /* Is this a procfd? */ > > > > + ret = -EINVAL; > > > > + if (!proc_is_tgid_procfd(f.file)) > > > > + goto err; > > > > > > -EBADF is the proper error code. > > Yeah, EINVAL tends to be used for bad flags... this is more about an > improper fd. > > > > > > > > + /* Without CONFIG_PROC_FS proc_pid() returns NULL. */ > > > > + pid = proc_pid(file_inode(f.file)); > > > > + if (!pid) > > > > + goto err; > > > > > > Perhaps you want to fold the proc_pid into the proc_is_tgid_procfd > > > call. That way proc_pid can stay private to proc. > > > > Hm, I guess we can do that for now. My intention was to have reuseable > > helpers but I guess it would be fine for now. > > > > > > > > > + if (!may_signal_procfd(pid)) > > > > + goto err; > > > > + > > Does the ns parent checking in may_signal_procfd need any locking or > RCU? I know pid and current namespaces are "pinned", but I don't know > how parent ns works here. I'm assuming the parents are stuck until all > children go away? Yeah, since they are hierarchical killing an ancestor means killing the children. Also, in case you're interested, there's precedent for that: kernel/pid_namespace.c:static struct ns_common *pidns_get_parent(struct ns_common *ns) I'm not using this function because a) I would have to special case the initial test-case and b) it takes a get() on the pid ns which would force us to use another put which is unnecessary. > > > > > + ret = kill_pid_info(sig, &kinfo, pid); > > Just double-checking for myself: this does not bypass > security_task_kill(), so no problem there AFAIK. > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> Thanks! :) As a sidenote I'm switching the name from procfd_send_signal() to taskfd_send_signal(). It seems to me the best way to handle Eric's request to reflect that we can eventually both signal tgids and tids. > > -- > Kees Cook
