From patchwork Fri Jun 7 14:17:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 10981893 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 24D2013AD for ; Fri, 7 Jun 2019 14:17:42 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 15A2B27EED for ; Fri, 7 Jun 2019 14:17:42 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1398428C4E; Fri, 7 Jun 2019 14:17:42 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 5B27C27EED for ; Fri, 7 Jun 2019 14:17:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729176AbfFGORg (ORCPT ); Fri, 7 Jun 2019 10:17:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58852 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728257AbfFGORf (ORCPT ); Fri, 7 Jun 2019 10:17:35 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E9C7E22389B; Fri, 7 Jun 2019 14:17:24 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-173.rdu2.redhat.com [10.10.120.173]) by smtp.corp.redhat.com (Postfix) with ESMTP id DC12578566; Fri, 7 Jun 2019 14:17:15 +0000 (UTC) Subject: [RFC][PATCH 00/13] Mount, FS, Block and Keyrings notifications [ver #4] From: David Howells To: viro@zeniv.linux.org.uk Cc: linux-usb@vger.kernel.org, linux-security-module@vger.kernel.org, Casey Schaufler , Stephen Smalley , Greg Kroah-Hartman , dhowells@redhat.com, raven@themaw.net, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-block@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 07 Jun 2019 15:17:10 +0100 Message-ID: <155991702981.15579.6007568669839441045.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 07 Jun 2019 14:17:35 +0000 (UTC) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Hi Al, Here's a set of patches to add a general variable-length notification queue concept and to add sources of events for: (1) Mount topology events, such as mounting, unmounting, mount expiry, mount reconfiguration. (2) Superblock events, such as R/W<->R/O changes, quota overrun and I/O errors (not complete yet). (3) Key/keyring events, such as creating, linking and removal of keys. (4) General device events (single common queue) including: - Block layer events, such as device errors - USB subsystem events, such as device/bus attach/remove, device reset, device errors. One of the reasons for this is so that we can remove the issue of processes having to repeatedly and regularly scan /proc/mounts, which has proven to be a system performance problem. To further aid this, the fsinfo() syscall on which this patch series depends, provides a way to access superblock and mount information in binary form without the need to parse /proc/mounts. LSM support is included, but controversial: (1) The creds of the process that did the fput() that reduced the refcount to zero are cached in the file struct. (2) __fput() overrides the current creds with the creds from (1) whilst doing the cleanup, thereby making sure that the creds seen by the destruction notification generated by mntput() appears to come from the last fputter. (3) security_post_notification() is called for each queue that we might want to post a notification into, thereby allowing the LSM to prevent covert communications. (?) Do I need to add security_set_watch(), say, to rule on whether a watch may be set in the first place? I might need to add a variant per watch-type. (?) Do I really need to keep track of the process creds in which an implicit object destruction happened? For example, imagine you create an fd with fsopen()/fsmount(). It is marked to dissolve the mount it refers to on close unless move_mount() clears that flag. Now, imagine someone looking at that fd through procfs at the same time as you exit due to an error. The LSM sees the destruction notification come from the looker if they happen to do their fput() after yours. Design decisions: (1) A misc chardev is used to create and open a ring buffer: fd = open("/dev/watch_queue", O_RDWR); which is then configured and mmap'd into userspace: ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE); ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter); buf = mmap(NULL, BUF_SIZE * page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); The fd cannot be read or written (though there is a facility to use write to inject records for debugging) and userspace just pulls data directly out of the buffer. (2) The ring index pointers are stored inside the ring and are thus accessible to userspace. Userspace should only update the tail pointer and never the head pointer or risk breaking the buffer. The kernel checks that the pointers appear valid before trying to use them. A 'skip' record is maintained around the pointers. (3) poll() can be used to wait for data to appear in the buffer. (4) Records in the buffer are binary, typed and have a length so that they can be of varying size. This means that multiple heterogeneous sources can share a common buffer. Tags may be specified when a watchpoint is created to help distinguish the sources. (5) The queue is reusable as there are 16 million types available, of which I've used 4, so there is scope for others to be used. (6) Records are filterable as types have up to 256 subtypes that can be individually filtered. Other filtration is also available. (7) Each time the buffer is opened, a new buffer is created - this means that there's no interference between watchers. (8) When recording a notification, the kernel will not sleep, but will rather mark a queue as overrun if there's insufficient space, thereby avoiding userspace causing the kernel to hang. (9) The 'watchpoint' should be specific where possible, meaning that you specify the object that you want to watch. (10) The buffer is created and then watchpoints are attached to it, using one of: keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01); mount_notify(AT_FDCWD, "/", 0, fd, 0x02); sb_notify(AT_FDCWD, "/mnt", 0, fd, 0x03); where in all three cases, fd indicates the queue and the number after is a tag between 0 and 255. (11) The watch must be removed if either the watch buffer is destroyed or the watched object is destroyed. Things I want to avoid: (1) Introducing features that make the core VFS dependent on the network stack or networking namespaces (ie. usage of netlink). (2) Dumping all this stuff into dmesg and having a daemon that sits there parsing the output and distributing it as this then puts the responsibility for security into userspace and makes handling namespaces tricky. Further, dmesg might not exist or might be inaccessible inside a container. (3) Letting users see events they shouldn't be able to see. Further things that could be considered: (1) Adding a keyctl call to allow a watch on a keyring to be extended to "children" of that keyring, such that the watch is removed from the child if it is unlinked from the keyring. (2) Adding global superblock event queue. (3) Propagating watches to child superblock over automounts. The patches can be found here also: http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=notifications Changes: v4: Split the basic UAPI bits out into their own patch and then split the LSM hooks out into an intermediate patch. Add LSM hooks for setting watches. Rename the *_notify() system calls to watch_*() for consistency. v3: I've added a USB notification source and reformulated the block notification source so that there's now a common watch list, for which the system call is now device_notify(). I've assigned a pair of unused ioctl numbers in the 'W' series to the ioctls added by this series. I've also added a description of the kernel API to the documentation. v2: I've fixed various issues raised by Jann Horn and GregKH and moved to krefs for refcounting. I've added some security features to try and give Casey Schaufler the LSM control he wants. David --- David Howells (13): security: Override creds in __fput() with last fputter's creds uapi: General notification ring definitions security: Add hooks to rule on setting a watch security: Add a hook for the point of notification insertion General notification queue with user mmap()'able ring buffer keys: Add a notification facility vfs: Add a mount-notification facility vfs: Add superblock notifications fsinfo: Export superblock notification counter Add a general, global device notification watch list block: Add block layer notifications usb: Add USB subsystem notifications Add sample notification program Documentation/ioctl/ioctl-number.txt | 1 Documentation/security/keys/core.rst | 58 ++ Documentation/watch_queue.rst | 492 ++++++++++++++++++ arch/x86/entry/syscalls/syscall_32.tbl | 3 arch/x86/entry/syscalls/syscall_64.tbl | 3 block/Kconfig | 9 block/blk-core.c | 29 + drivers/base/Kconfig | 9 drivers/base/Makefile | 1 drivers/base/watch.c | 89 +++ drivers/misc/Kconfig | 13 drivers/misc/Makefile | 1 drivers/misc/watch_queue.c | 889 ++++++++++++++++++++++++++++++++ drivers/usb/core/Kconfig | 10 drivers/usb/core/devio.c | 55 ++ drivers/usb/core/hub.c | 3 fs/Kconfig | 21 + fs/Makefile | 1 fs/file_table.c | 12 fs/fsinfo.c | 12 fs/mount.h | 33 + fs/mount_notify.c | 187 +++++++ fs/namespace.c | 9 fs/super.c | 122 ++++ include/linux/blkdev.h | 15 + include/linux/dcache.h | 1 include/linux/device.h | 7 include/linux/fs.h | 79 +++ include/linux/key.h | 4 include/linux/lsm_hooks.h | 48 ++ include/linux/security.h | 35 + include/linux/syscalls.h | 5 include/linux/usb.h | 19 + include/linux/watch_queue.h | 87 +++ include/uapi/linux/fsinfo.h | 10 include/uapi/linux/keyctl.h | 1 include/uapi/linux/watch_queue.h | 213 ++++++++ kernel/sys_ni.c | 7 samples/Kconfig | 6 samples/Makefile | 1 samples/vfs/test-fsinfo.c | 13 samples/watch_queue/Makefile | 9 samples/watch_queue/watch_test.c | 308 +++++++++++ security/keys/Kconfig | 10 security/keys/compat.c | 2 security/keys/gc.c | 5 security/keys/internal.h | 30 + security/keys/key.c | 37 + security/keys/keyctl.c | 95 +++ security/keys/keyring.c | 17 - security/keys/request_key.c | 4 security/security.c | 29 + 52 files changed, 3121 insertions(+), 38 deletions(-) create mode 100644 Documentation/watch_queue.rst create mode 100644 drivers/base/watch.c create mode 100644 drivers/misc/watch_queue.c create mode 100644 fs/mount_notify.c create mode 100644 include/linux/watch_queue.h create mode 100644 include/uapi/linux/watch_queue.h create mode 100644 samples/watch_queue/Makefile create mode 100644 samples/watch_queue/watch_test.c