From patchwork Wed Jul 15 14:49:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Adrian Reber X-Patchwork-Id: 11665593 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 113BF13B1 for ; Wed, 15 Jul 2020 14:51:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E77B7206F5 for ; Wed, 15 Jul 2020 14:51:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HLiDjGs/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726694AbgGOOvX (ORCPT ); Wed, 15 Jul 2020 10:51:23 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:53250 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726634AbgGOOvX (ORCPT ); Wed, 15 Jul 2020 10:51:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594824681; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qgiW7ncb5vtKY1UKZKCcWEcewAM6ZIUsPgJWUmthSs0=; b=HLiDjGs/rCZIhhleCBRnz9OoD8Ld/keMxI0fcRBYGPtZzEdzO8LUbhXvLLZWxxAQRwiSAK eGn1W2AQuxOiyBnCeCSwmCfBxR6WZ4hKwmqpHifx1oix8tbGYZcrPnMO+G0PaUqCBZWwQl bb4YEvFHx9pIZQoLyCIMDFGGebyIeF4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-107-_EpRdUJqN-GvLVGG7SHwHQ-1; Wed, 15 Jul 2020 10:51:15 -0400 X-MC-Unique: _EpRdUJqN-GvLVGG7SHwHQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E4A01100960F; Wed, 15 Jul 2020 14:51:11 +0000 (UTC) Received: from dcbz.redhat.com (ovpn-114-113.ams2.redhat.com [10.36.114.113]) by smtp.corp.redhat.com (Postfix) with ESMTP id A43E360BF1; Wed, 15 Jul 2020 14:51:04 +0000 (UTC) From: Adrian Reber To: Christian Brauner , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, Andrei Vagin , Nicolas Viennot , =?utf-8?b?TWljaGHFgiBDxYJh?= =?utf-8?b?cGnFhHNraQ==?= , Kamil Yurtsever , Dirk Petersen , Christine Flood , Casey Schaufler Cc: Mike Rapoport , Radostin Stoyanov , Adrian Reber , Cyrill Gorcunov , Serge Hallyn , Stephen Smalley , Sargun Dhillon , Arnd Bergmann , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, Eric Paris , Jann Horn , linux-fsdevel@vger.kernel.org Subject: [PATCH v5 1/6] capabilities: Introduce CAP_CHECKPOINT_RESTORE Date: Wed, 15 Jul 2020 16:49:49 +0200 Message-Id: <20200715144954.1387760-2-areber@redhat.com> In-Reply-To: <20200715144954.1387760-1-areber@redhat.com> References: <20200715144954.1387760-1-areber@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: This patch introduces CAP_CHECKPOINT_RESTORE, a new capability facilitating checkpoint/restore for non-root users. Over the last years, The CRIU (Checkpoint/Restore In Userspace) team has been asked numerous times if it is possible to checkpoint/restore a process as non-root. The answer usually was: 'almost'. The main blocker to restore a process as non-root was to control the PID of the restored process. This feature available via the clone3 system call, or via /proc/sys/kernel/ns_last_pid is unfortunately guarded by CAP_SYS_ADMIN. In the past two years, requests for non-root checkpoint/restore have increased due to the following use cases: * Checkpoint/Restore in an HPC environment in combination with a resource manager distributing jobs where users are always running as non-root. There is a desire to provide a way to checkpoint and restore long running jobs. * Container migration as non-root * We have been in contact with JVM developers who are integrating CRIU into a Java VM to decrease the startup time. These checkpoint/restore applications are not meant to be running with CAP_SYS_ADMIN. We have seen the following workarounds: * Use a setuid wrapper around CRIU: See https://github.com/FredHutch/slurm-examples/blob/master/checkpointer/lib/checkpointer/checkpointer-suid.c * Use a setuid helper that writes to ns_last_pid. Unfortunately, this helper delegation technique is impossible to use with clone3, and is thus prone to races. See https://github.com/twosigma/set_ns_last_pid * Cycle through PIDs with fork() until the desired PID is reached: This has been demonstrated to work with cycling rates of 100,000 PIDs/s See https://github.com/twosigma/set_ns_last_pid * Patch out the CAP_SYS_ADMIN check from the kernel * Run the desired application in a new user and PID namespace to provide a local CAP_SYS_ADMIN for controlling PIDs. This technique has limited use in typical container environments (e.g., Kubernetes) as /proc is typically protected with read-only layers (e.g., /proc/sys) for hardening purposes. Read-only layers prevent additional /proc mounts (due to proc's SB_I_USERNS_VISIBLE property), making the use of new PID namespaces limited as certain applications need access to /proc matching their PID namespace. The introduced capability allows to: * Control PIDs when the current user is CAP_CHECKPOINT_RESTORE capable for the corresponding PID namespace via ns_last_pid/clone3. * Open files in /proc/pid/map_files when the current user is CAP_CHECKPOINT_RESTORE capable in the root namespace, useful for recovering files that are unreachable via the file system such as deleted files, or memfd files. See corresponding selftest for an example with clone3(). Signed-off-by: Adrian Reber Signed-off-by: Nicolas Viennot Acked-by: Christian Brauner --- include/linux/capability.h | 6 ++++++ include/uapi/linux/capability.h | 9 ++++++++- security/selinux/include/classmap.h | 5 +++-- 3 files changed, 17 insertions(+), 3 deletions(-) diff --git a/include/linux/capability.h b/include/linux/capability.h index b4345b38a6be..1e7fe311cabe 100644 --- a/include/linux/capability.h +++ b/include/linux/capability.h @@ -261,6 +261,12 @@ static inline bool bpf_capable(void) return capable(CAP_BPF) || capable(CAP_SYS_ADMIN); } +static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns) +{ + return ns_capable(ns, CAP_CHECKPOINT_RESTORE) || + ns_capable(ns, CAP_SYS_ADMIN); +} + /* audit system wants to get cap info from files as well */ extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps); diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h index 48ff0757ae5e..395dd0df8d08 100644 --- a/include/uapi/linux/capability.h +++ b/include/uapi/linux/capability.h @@ -408,7 +408,14 @@ struct vfs_ns_cap_data { */ #define CAP_BPF 39 -#define CAP_LAST_CAP CAP_BPF + +/* Allow checkpoint/restore related operations */ +/* Allow PID selection during clone3() */ +/* Allow writing to ns_last_pid */ + +#define CAP_CHECKPOINT_RESTORE 40 + +#define CAP_LAST_CAP CAP_CHECKPOINT_RESTORE #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP) diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index e54d62d529f1..ba2e01a6955c 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -27,9 +27,10 @@ "audit_control", "setfcap" #define COMMON_CAP2_PERMS "mac_override", "mac_admin", "syslog", \ - "wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf" + "wake_alarm", "block_suspend", "audit_read", "perfmon", "bpf", \ + "checkpoint_restore" -#if CAP_LAST_CAP > CAP_BPF +#if CAP_LAST_CAP > CAP_CHECKPOINT_RESTORE #error New capability defined, please update COMMON_CAP2_PERMS. #endif