From patchwork Thu Dec 26 18:02:30 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sargun Dhillon X-Patchwork-Id: 11310643 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id AF2A414E3 for ; Thu, 26 Dec 2019 18:02:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7BE5D20722 for ; Thu, 26 Dec 2019 18:02:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=sargun.me header.i=@sargun.me header.b="fS/sLofa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726586AbfLZSCe (ORCPT ); Thu, 26 Dec 2019 13:02:34 -0500 Received: from mail-il1-f196.google.com ([209.85.166.196]:41186 "EHLO mail-il1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726480AbfLZSCd (ORCPT ); Thu, 26 Dec 2019 13:02:33 -0500 Received: by mail-il1-f196.google.com with SMTP id f10so20675941ils.8 for ; Thu, 26 Dec 2019 10:02:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sargun.me; s=google; h=date:from:to:cc:subject:message-id:mime-version:content-disposition :user-agent; bh=ONw/OL8JM4aZSJthnLMZow64GW9EQFEy/ugd4rWw17I=; b=fS/sLofaF5GDeJwaGiikpY1J3oGIbpB636hMkrOdwpxj4DA1W1Or+EdACFDbS9WupK dgAcbe3m1M1NFUVP1i/apRh9S04msHnLXHKpcD8unFgvlT1DrziaZFMBJno25LO4bjsH aYP6ibMlnCthZDCmIVYN/BE6YPb3qdCuOvhXI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition:user-agent; bh=ONw/OL8JM4aZSJthnLMZow64GW9EQFEy/ugd4rWw17I=; b=ts4CNXwC/d9dfFOQC93DrIHaAXn1dGtc+HSIT+617qqxJ9ui1ymebrC5SZrsqQDOQN Yg3sjCV7wzaxJGoWq/mWfufTTslmLlOxtECQmfQ1yCTwdkKI9v8rHxFQkYAIKkV7yHv/ kznaT7C8VnMH9qkD08ev4m3rOyCScN2LOef6QadOs51Ah6Xkscnb0qFYNlSflP5RvK0Y 685wbRQyXeS87/aGxjOo5M9QXCwnnPBgQSY/azpwn7O288UP+qjw1PJ3dEi0bbmH5OMm EPJNUB2+CnKpa5TMHvOH7jW3EqEWZfZ7lbA2YYUSHj0215dpYUsuQbcMGghhnFPVHHwp 2cMw== X-Gm-Message-State: APjAAAU41xoWUzMGea9R8obNtz/Z1RBl2YM8Q6ajzFFM8jZsjo2hrbdF N8eRvhRj4CHtjd9ckmEcRN1uYg== X-Google-Smtp-Source: APXvYqz+/WtdlSrA/8bsDAuNVYEG8mox8GoQRc4mAHzJ05cj8TnZxW+3gtSpINmFkqyhgbcmCaLuDA== X-Received: by 2002:a92:d151:: with SMTP id t17mr24010974ilg.175.1577383352464; Thu, 26 Dec 2019 10:02:32 -0800 (PST) Received: from ircssh-2.c.rugged-nimbus-611.internal (80.60.198.104.bc.googleusercontent.com. [104.198.60.80]) by smtp.gmail.com with ESMTPSA id 75sm12426869ila.61.2019.12.26.10.02.31 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 26 Dec 2019 10:02:31 -0800 (PST) Date: Thu, 26 Dec 2019 18:02:30 +0000 From: Sargun Dhillon To: linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org Cc: tycho@tycho.ws, jannh@google.com, cyphar@cyphar.com, christian.brauner@ubuntu.com, oleg@redhat.com, luto@amacapital.net, viro@zeniv.linux.org.uk, gpascutto@mozilla.com, ealvarez@mozilla.com, fweimer@redhat.com, jld@mozilla.com, arnd@arndb.de Subject: [PATCH v7 0/3] Add pidfd_getfd syscall Message-ID: <20191226180227.GA29389@ircssh-2.c.rugged-nimbus-611.internal> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org This patchset introduces a mechanism (pidfd_getfd syscall) to get file descriptors from other processes via pidfd. Although this can be achieved using SCM_RIGHTS, and parasitic code injection, this offers a more straightforward mechanism, with less overhead and complexity. The process under manipulation's fd still remains valid, and unmodified by the copy operation. It introduces a flags field. The flags field is reserved a the moment, but the intent is to extend it with the following capabilities: * Close the remote FD when copying it * Drop the cgroup data if it's a fd pointing a socket when copying it The syscall numbers were chosen to be one greater than openat2. Summary of history: This initially started as a ptrace command. It did not require the process to be stopped, and felt like kind of an awkward fit for ptrace. After that, it moved to an ioctl on the pidfd. Given functionality, it made sense to make it a syscall which did not require the process to be stopped. Previous versions: V6: https://lore.kernel.org/lkml/20191223210823.GA25083@ircssh-2.c.rugged-nimbus-611.internal/ V5: https://lore.kernel.org/lkml/20191220232746.GA20215@ircssh-2.c.rugged-nimbus-611.internal/ V4: https://lore.kernel.org/lkml/20191218235310.GA17259@ircssh-2.c.rugged-nimbus-611.internal/ V3: https://lore.kernel.org/lkml/20191217005842.GA14379@ircssh-2.c.rugged-nimbus-611.internal/ V2: https://lore.kernel.org/lkml/20191209070446.GA32336@ircssh-2.c.rugged-nimbus-611.internal/ RFC V1: https://lore.kernel.org/lkml/20191205234450.GA26369@ircssh-2.c.rugged-nimbus-611.internal/ Changes since v6: * Proper attribution of get_task_file helper * Move all types for syscall to int to represent fd Changes since v5: * Drop pidfd_getfd_options struct and replace with a flags field Changes since v4: * Turn into a syscall * Move to PTRACE_MODE_ATTACH_REALCREDS from PTRACE_MODE_READ_REALCREDS * Remove the sample code. This will come in another patchset, as the new self-tests cover all the functionality. Changes since v3: * Add self-test * Move to ioctl passing fd directly, versus args struct * Shuffle around include files Changes since v2: * Move to ioctl on pidfd instead of ptrace function * Add security check before moving file descriptor Changes since the RFC v1: * Introduce a new helper to fs/file.c to fetch a file descriptor from any process. It largely uses the code suggested by Oleg, with a few changes to fix locking * It uses an extensible options struct to supply the FD, and option. * I added a sample, using the code from the user-ptrace sample Sargun Dhillon (3): vfs, fdtable: Add get_task_file helper pid: Introduce pidfd_getfd syscall test: Add test for pidfd getfd arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/file.c | 21 +- include/linux/file.h | 2 + include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 4 +- kernel/pid.c | 103 +++++++ tools/testing/selftests/pidfd/.gitignore | 1 + tools/testing/selftests/pidfd/Makefile | 2 +- .../selftests/pidfd/pidfd_getfd_test.c | 254 ++++++++++++++++++ 26 files changed, 403 insertions(+), 5 deletions(-) create mode 100644 tools/testing/selftests/pidfd/pidfd_getfd_test.c