From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C599C43603 for ; Thu, 19 Dec 2019 08:03:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D336F24650 for ; Thu, 19 Dec 2019 08:03:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726648AbfLSID3 (ORCPT ); Thu, 19 Dec 2019 03:03:29 -0500 Received: from mout.kundenserver.de ([212.227.126.134]:53755 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbfLSID3 (ORCPT ); Thu, 19 Dec 2019 03:03:29 -0500 Received: from mail-qk1-f174.google.com ([209.85.222.174]) by mrelayeu.kundenserver.de (mreue010 [212.227.15.129]) with ESMTPSA (Nemesis) id 1M6lUk-1ibnpx1XRO-008KmM; Thu, 19 Dec 2019 09:03:27 +0100 Received: by mail-qk1-f174.google.com with SMTP id z14so2675913qkg.9; Thu, 19 Dec 2019 00:03:26 -0800 (PST) X-Gm-Message-State: APjAAAV49yOs3eUl8ZUzbvhQ7rduRPS6YNXnz/QjcYdF2zy63nd1XpP1 sUFjPcjrlMZnKPJLYtcRYp+y0fmax9CmfWLSdjQ= X-Google-Smtp-Source: APXvYqxXQF6sR2skniit5JgCT5kH+gYfBPMf8t/20i/mEzMIIkYTsPQO26NNE6VO7z/gvWUC1MyADsYJWrkMuIMYl9A= X-Received: by 2002:a37:a8d4:: with SMTP id r203mr6933223qke.394.1576742606043; Thu, 19 Dec 2019 00:03:26 -0800 (PST) MIME-Version: 1.0 References: <20191218235459.GA17271@ircssh-2.c.rugged-nimbus-611.internal> In-Reply-To: <20191218235459.GA17271@ircssh-2.c.rugged-nimbus-611.internal> From: Arnd Bergmann Date: Thu, 19 Dec 2019 09:03:09 +0100 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 2/5] pid: Add PIDFD_IOCTL_GETFD to fetch file descriptors from processes To: Sargun Dhillon Cc: "linux-kernel@vger.kernel.org" , Linux Containers , Linux API , Linux FS-devel Mailing List , Tycho Andersen , Jann Horn , Aleksa Sarai , Christian Brauner , Oleg Nesterov , Andy Lutomirski , Al Viro , gpascutto@mozilla.com, ealvarez@mozilla.com, Florian Weimer , jld@mozilla.com Content-Type: text/plain; charset="UTF-8" X-Provags-ID: V03:K1:IiokMjtel7Ht/qXKLtr7vWPyiJm5ObDabfNBLD0croeK4+f9DuZ R4eTY4HQL06tF0ng7Ld5H++ri/uZgzWaJ+EmX5gMrtOQAjul7+vqHo0mIj1uuk/OYHV0LBh +7qV0XseDO18FgfrNaWZXF43LUBacU3SUqB3SfBKzpjQMNIOlg6flwUcPCkaK9DvkNHgnH4 ijGS8Hl9D4poXlab8qnDQ== X-UI-Out-Filterresults: notjunk:1;V03:K0:/bWUbbeESK4=:K3P5dPIBMosadcWX12v0Wf yecallTrqRqcbthXQiUfh7uxcJtfno+hmx6KezWAQGmF8UcFy0IAK/b7FHOTu5cajmdNdRKlS iwEVHS4nIze351xxRhP++RS4dtYTZAwdRFjLG8j1fZaTmyyEQu5J0Us43xbI0zC74lRdhjIZx EyG2A6HykJ5TH7ndEG9qVU6hcOzSsHzAMd7Ji78Qmu43GytKjbNrUAVTF/Nhvn349u+RTf79F DF+NTIWscDSXjxd0/T4F31m9rkB5JzBnrQgM1XCQ4+r86liyV+L5nSQos3uIl+m3GcOvJ00rf PqJatkAoxsDUDftTPLWXt/AOywxVAMv6dHftP1K1wHm5FM19EIHhLpFw9IJ1KwsOr8ZOG9o+B YLu6LHgEYSlqrujH7xGvC+5AXenIQ9KAb+9eIa/Lr4uATB/JxZz1xl/hYUKXQ+NShRlwrA1GY ggvS65TgSSGq5ro8jhI5zIQI+80WexLwul4jFG0mnoKXNic2I9IcNyPJjuQkOBZnfAKegP+fo UFpOrNGeGDuDC1SJUIkce6np4967tD05UkpunImNv5uWVIlN9dD5vnJhUj5HcBHgUGCo6RYKY mWqApzVcw8L0RVxeZ0CF0CV+X+HNRVEyEESSmh7pvapslmU49KgKKDjtClwOdCxYnimmZbRqG YDVkKWkJ5M3z5+8BH73PIERQNWfQLCsK+RkZO5gyWicPwF9D7AFA7vhFi4RLJBbh2C4yTjmxi jl76bxcloBA1gp1QQqGdApvLD723BVFyPAViT3vdMaDbvS3aYZ21ZVsVrkJKA3BiU3MwDQIok 1wiQmDC0HAQGypikE+76GnqlVbWf/IXXFxQcfH4XjC8qarX1OoS1nOwiF+XYHgXSde22cbQ/n xfKAz6ePdJcbSD6VPc+g== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 19, 2019 at 12:55 AM Sargun Dhillon wrote: > +#define PIDFD_IOCTL_GETFD _IOWR('p', 0xb0, __u32) This describes an ioctl command that reads and writes a __u32 variable using a pointer passed as the argument, which doesn't match the implementation: > +static long pidfd_getfd(struct pid *pid, u32 fd) > +{ ... > + return retfd; This function passes an fd as the argument and returns a new fd, so the command number would be #define PIDFD_IOCTL_GETFD _IO('p', 0xb0) While this implementation looks easy enough, and it is roughly what I would do in case of a system call, I would recommend for an ioctl implementation to use the __u32 pointer instead: static long pidfd_getfd_ioctl(struct pid *pid, u32 __user *arg) { int their_fd, new_fd; int ret; ret = get_user(their_fd, arg); if (ret) return ret; new_fd = pidfd_getfd(pid, their_fd); if (new_fd < 0) return new_fd; return put_user(new_fd, arg); } Direct argument passing in ioctls may confuse readers because it is fairly unusual, and it doesn't work with this: > const struct file_operations pidfd_fops = { > .release = pidfd_release, > .poll = pidfd_poll, > + .unlocked_ioctl = pidfd_ioctl, > + .compat_ioctl = compat_ptr_ioctl, compat_ptr_ioctl() only works if the argument is a pointer, as it mangles the argument to turn it from a 32-bit pointer value into a 64-bit pointer value. These are almost always the same (arch/s390 being the sole exception), but you should not rely on it. For now it would be find to do '.compat_ioctl = pidfd_ioctl', but that in turn is wrong if you ever add another ioctl command that does pass a pointer. Arnd