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From: Dongsu Park <dongsu@kinvolk.io>
To: linux-kernel@vger.kernel.org
Cc: containers@lists.linux-foundation.org,
	Alban Crequy <alban@kinvolk.io>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Miklos Szeredi <mszeredi@redhat.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	Sargun Dhillon <sargun@sargun.me>,
	Dongsu Park <dongsu@kinvolk.io>
Subject: [PATCH v5 00/11] FUSE mounts from non-init user namespaces
Date: Fri, 22 Dec 2017 15:32:24 +0100
Message-ID: <cover.1512741134.git.dongsu@kinvolk.io> (raw)

This patchset v5 is based on work by Seth Forshee and Eric Biederman.
The latest patchset was v4:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1132206.html

At the moment, filesystems backed by physical medium can only be mounted
by real root in the initial user namespace. This restriction exists
because if it's allowed for root user in non-init user namespaces to
mount the filesystem, then it effectively allows the user to control the
underlying source of the filesystem. In case of FUSE, the source would
mean any underlying device.

However, in many use cases such as containers, it's necessary to allow
filesystems to be mounted from non-init user namespaces. Goal of this
patchset is to allow FUSE filesystems to be mounted from non-init user
namespaces. Support for other filesystems like ext4 are not in the
scope of this patchset.

Let me describe how to test mounting from non-init user namespaces. It's
assumed that tests are done via sshfs, a userspace filesystem based on
FUSE with ssh as backend. Testing system is Fedora 27.

====
$ sudo dnf install -y sshfs
$ sudo mkdir -p /mnt/userns

### workaround to get the sshfs permission checks
$ sudo chown -R $UID:$UID /etc/ssh/ssh_config.d /usr/share/crypto-policies

$ unshare -U -r -m
# sshfs root@localhost: /mnt/userns

### You can see sshfs being mounted from a non-init user namespace
# mount | grep sshfs
root@localhost: on /mnt/userns type fuse.sshfs
(rw,nosuid,nodev,relatime,user_id=0,group_id=0)

# touch /mnt/userns/test
# ls -l /mnt/userns/test
-rw-r--r-- 1 root root 0 Dec 11 19:01 /mnt/userns/test
====

Open another terminal, check the mountpoint from outside the namespace.

====
$ grep userns /proc/$(pidof sshfs)/mountinfo
131 102 0:35 / /mnt/userns rw,nosuid,nodev,relatime - fuse.sshfs
root@localhost: rw,user_id=0,group_id=0
====

After all tests are done, you can unmount the filesystem
inside the namespace.

====
# fusermount -u /mnt/userns
====

Changes since v4:
 * Remove other parts like ext4 to keep the patchset minimal for FUSE
 * Add and change commit messages
 * Describe how to test non-init user namespaces

TODO:
 * Think through potential security implications. There are 2 patches
   being prepared for security issues. One is "ima: define a new policy
   option named force" by Mimi Zohar, which adds an option to specify
   that the results should not be cached:
   https://marc.info/?l=linux-integrity&m=151275680115856&w=2
   The other one is to basically prevent FUSE results from being cached,
   which is still in progress.

 * Test IMA/LSMs. Details are written in
   https://github.com/kinvolk/fuse-userns-patches/blob/master/tests/TESTING_INTEGRITY.md

Patches 1-2 deal with an additional flag of lookup_bdev() to check for
additional inode permission.

Patches 3-7 allow the superblock owner to change ownership of inodes, and
deal with additional capability checks w.r.t user namespaces.

Patches 8-10 allow FUSE filesystems to be mounted outside of the init
user namespace.

Patch 11 handles a corner case of non-root users in EVM.

The patchset is also available in our github repo:
  https://github.com/kinvolk/linux/tree/dongsu/fuse-userns-v5-1


Eric W. Biederman (1):
  fs: Allow superblock owner to change ownership of inodes

Seth Forshee (10):
  block_dev: Support checking inode permissions in lookup_bdev()
  mtd: Check permissions towards mtd block device inode when mounting
  fs: Don't remove suid for CAP_FSETID for userns root
  fs: Allow superblock owner to access do_remount_sb()
  capabilities: Allow privileged user in s_user_ns to set security.*
    xattrs
  fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems
  fuse: Support fuse filesystems outside of init_user_ns
  fuse: Restrict allow_other to the superblock's namespace or a
    descendant
  fuse: Allow user namespace mounts
  evm: Don't update hmacs in user ns mounts

 drivers/md/bcache/super.c           |  2 +-
 drivers/md/dm-table.c               |  2 +-
 drivers/mtd/mtdsuper.c              |  6 +++++-
 fs/attr.c                           | 34 ++++++++++++++++++++++++++--------
 fs/block_dev.c                      | 13 ++++++++++---
 fs/fuse/cuse.c                      |  3 ++-
 fs/fuse/dev.c                       | 11 ++++++++---
 fs/fuse/dir.c                       | 16 ++++++++--------
 fs/fuse/fuse_i.h                    |  6 +++++-
 fs/fuse/inode.c                     | 35 +++++++++++++++++++++--------------
 fs/inode.c                          |  6 ++++--
 fs/ioctl.c                          |  4 ++--
 fs/namespace.c                      |  4 ++--
 fs/proc/base.c                      |  7 +++++++
 fs/proc/generic.c                   |  7 +++++++
 fs/proc/proc_sysctl.c               |  7 +++++++
 fs/quota/quota.c                    |  2 +-
 include/linux/fs.h                  |  2 +-
 kernel/user_namespace.c             |  1 +
 security/commoncap.c                |  8 ++++++--
 security/integrity/evm/evm_crypto.c |  3 ++-
 21 files changed, 127 insertions(+), 52 deletions(-)

-- 
2.13.6

             reply index

Thread overview: 107+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-22 14:32 Dongsu Park [this message]
2017-12-22 14:32 ` [PATCH 01/11] block_dev: Support checking inode permissions in lookup_bdev() Dongsu Park
2017-12-22 18:59   ` Coly Li
2017-12-23 12:00     ` Dongsu Park
2017-12-23  3:03   ` Serge E. Hallyn
2017-12-22 14:32 ` [PATCH 02/11] mtd: Check permissions towards mtd block device inode when mounting Dongsu Park
2017-12-22 21:06   ` Richard Weinberger
2017-12-23 12:18     ` Dongsu Park
2017-12-23 12:56       ` Richard Weinberger
2017-12-23  3:05   ` Serge E. Hallyn
2017-12-22 14:32 ` [PATCH 03/11] fs: Allow superblock owner to change ownership of inodes Dongsu Park
2017-12-23  3:17   ` Serge E. Hallyn
2018-01-05 19:24   ` Luis R. Rodriguez
2018-01-09 15:10     ` Dongsu Park
2018-01-09 17:23       ` Luis R. Rodriguez
2018-02-13 13:18   ` Miklos Szeredi
2018-02-16 22:00     ` Eric W. Biederman
2017-12-22 14:32 ` [PATCH 04/11] fs: Don't remove suid for CAP_FSETID for userns root Dongsu Park
2017-12-23  3:26   ` Serge E. Hallyn
2017-12-23 12:38     ` Dongsu Park
2018-02-13 13:37       ` Miklos Szeredi
2017-12-22 14:32 ` [PATCH 05/11] fs: Allow superblock owner to access do_remount_sb() Dongsu Park
2017-12-23  3:30   ` Serge E. Hallyn
2017-12-22 14:32 ` [PATCH 06/11] capabilities: Allow privileged user in s_user_ns to set security.* xattrs Dongsu Park
2017-12-23  3:33   ` Serge E. Hallyn
2017-12-22 14:32 ` [PATCH 07/11] fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems Dongsu Park
2017-12-23  3:39   ` Serge E. Hallyn
2018-02-14 12:28   ` Miklos Szeredi
2018-02-19 22:56     ` Eric W. Biederman
2017-12-22 14:32 ` [PATCH 08/11] fuse: Support fuse filesystems outside of init_user_ns Dongsu Park
2017-12-23  3:46   ` Serge E. Hallyn
2018-01-17 10:59   ` Alban Crequy
2018-01-17 14:29     ` Seth Forshee
2018-01-17 18:56       ` Alban Crequy
2018-01-17 19:31         ` Seth Forshee
2018-01-18 10:29           ` Alban Crequy
2018-02-12 15:57   ` Miklos Szeredi
2018-02-12 16:35     ` Eric W. Biederman
2018-02-13 10:20       ` Miklos Szeredi
2018-02-16 21:52         ` Eric W. Biederman
2018-02-20  2:12   ` Eric W. Biederman
2017-12-22 14:32 ` [PATCH 09/11] fuse: Restrict allow_other to the superblock's namespace or a descendant Dongsu Park
2017-12-23  3:50   ` Serge E. Hallyn
2018-02-19 23:16   ` Eric W. Biederman
2017-12-22 14:32 ` [PATCH 10/11] fuse: Allow user namespace mounts Dongsu Park
2017-12-23  3:51   ` Serge E. Hallyn
2018-02-14 13:44   ` Miklos Szeredi
2018-02-15  8:46     ` Miklos Szeredi
2017-12-22 14:32 ` [PATCH 11/11] evm: Don't update hmacs in user ns mounts Dongsu Park
2017-12-23  4:03   ` Serge E. Hallyn
2017-12-24  5:12     ` Mimi Zohar
2017-12-24  5:56       ` Mimi Zohar
2017-12-25  7:05 ` [PATCH v5 00/11] FUSE mounts from non-init user namespaces Eric W. Biederman
2018-01-09 15:05   ` Dongsu Park
2018-01-18 14:58     ` Alban Crequy
2018-02-19 23:09       ` Eric W. Biederman
2018-02-13 11:32 ` Miklos Szeredi
2018-02-16 21:53   ` Eric W. Biederman
2018-02-21 20:24 ` [PATCH v6 0/6] fuse: " Eric W. Biederman
2018-02-21 20:29   ` [PATCH v6 1/5] fuse: Remove the buggy retranslation of pids in fuse_dev_do_read Eric W. Biederman
2018-02-22 10:13     ` Miklos Szeredi
2018-02-22 19:04       ` Eric W. Biederman
2018-02-21 20:29   ` [PATCH v6 2/5] fuse: Fail all requests with invalid uids or gids Eric W. Biederman
2018-02-22 10:26     ` Miklos Szeredi
2018-02-22 18:15       ` Eric W. Biederman
2018-02-21 20:29   ` [PATCH v6 3/5] fuse: Support fuse filesystems outside of init_user_ns Eric W. Biederman
2018-02-21 20:29   ` [PATCH v6 4/5] fuse: Ensure posix acls are translated " Eric W. Biederman
2018-02-22 11:40     ` Miklos Szeredi
2018-02-22 19:18       ` Eric W. Biederman
2018-02-22 22:50         ` Eric W. Biederman
2018-02-26  7:47           ` Miklos Szeredi
2018-02-26 16:35             ` Eric W. Biederman
2018-02-26 21:51               ` Eric W. Biederman
2018-02-21 20:29   ` [PATCH v6 5/5] fuse: Restrict allow_other to the superblock's namespace or a descendant Eric W. Biederman
2018-02-26 23:52   ` [PATCH v7 0/7] fuse: mounts from non-init user namespaces Eric W. Biederman
2018-02-26 23:52     ` [PATCH v7 1/7] fuse: Remove the buggy retranslation of pids in fuse_dev_do_read Eric W. Biederman
2018-02-26 23:52     ` [PATCH v7 2/7] fuse: Fail all requests with invalid uids or gids Eric W. Biederman
2018-02-26 23:52     ` [PATCH v7 3/7] fs/posix_acl: Document that get_acl respects ACL_DONT_CACHE Eric W. Biederman
2018-02-27  1:13       ` Linus Torvalds
2018-02-27  2:53         ` Eric W. Biederman
2018-02-27  3:14           ` Eric W. Biederman
2018-02-27  3:41             ` Linus Torvalds
2018-03-02 19:53               ` [RFC][PATCH] fs/posix_acl: Update the comments and support lightweight cache skipping Eric W. Biederman
2018-02-27  3:36           ` [PATCH v7 3/7] fs/posix_acl: Document that get_acl respects ACL_DONT_CACHE Linus Torvalds
2018-02-26 23:52     ` [PATCH v7 4/7] fuse: Cache a NULL acl when FUSE_GETXATTR returns -ENOSYS Eric W. Biederman
2018-02-26 23:53     ` [PATCH v7 5/7] fuse: Simplfiy the posix acl handling logic Eric W. Biederman
2018-02-27  9:00       ` Miklos Szeredi
2018-03-02 21:49         ` Eric W. Biederman
2018-02-26 23:53     ` [PATCH v7 6/7] fuse: Support fuse filesystems outside of init_user_ns Eric W. Biederman
2018-02-26 23:53     ` [PATCH v7 7/7] fuse: Restrict allow_other to the superblock's namespace or a descendant Eric W. Biederman
2018-03-02 21:58     ` [PATCH v8 0/6] fuse: mounts from non-init user namespaces Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 1/6] fs/posix_acl: Update the comments and support lightweight cache skipping Eric W. Biederman
2018-03-05  9:53         ` Miklos Szeredi
2018-03-05 13:53           ` Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 2/6] fuse: Simplfiy the posix acl handling logic Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 3/6] fuse: Remove the buggy retranslation of pids in fuse_dev_do_read Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 4/6] fuse: Fail all requests with invalid uids or gids Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 5/6] fuse: Support fuse filesystems outside of init_user_ns Eric W. Biederman
2018-03-02 21:59       ` [PATCH v8 6/6] fuse: Restrict allow_other to the superblock's namespace or a descendant Eric W. Biederman
2018-03-08 21:23       ` [PATCH v9 0/4] fuse: mounts from non-init user namespaces Eric W. Biederman
2018-03-08 21:24         ` [PATCH v9 1/4] fuse: Remove the buggy retranslation of pids in fuse_dev_do_read Eric W. Biederman
2018-03-08 21:24         ` [PATCH v9 2/4] fuse: Fail all requests with invalid uids or gids Eric W. Biederman
2018-03-08 21:24         ` [PATCH v9 3/4] fuse: Support fuse filesystems outside of init_user_ns Eric W. Biederman
2018-03-08 21:24         ` [PATCH v9 4/4] fuse: Restrict allow_other to the superblock's namespace or a descendant Eric W. Biederman
2018-03-20 16:25         ` [PATCH v9 0/4] fuse: mounts from non-init user namespaces Miklos Szeredi
2018-03-20 18:27           ` Eric W. Biederman
2018-03-21  8:38             ` Miklos Szeredi

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