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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: linux-security-module@vger.kernel.org,
	Kees Cook <keescook@chromium.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	linux-api@vger.kernel.org, containers@lists.linux-foundation.org,
	Jann Horn <jannh@google.com>,
	linux-kernel@vger.kernel.org, smbarber@chromium.org,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v2 00/28] user_namespace: introduce fsid mappings
Date: Mon, 17 Feb 2020 14:35:38 -0800	[thread overview]
Message-ID: <1581978938.24289.18.camel@HansenPartnership.com> (raw)
In-Reply-To: <20200217212022.2rfex3qsdjyyqrq7@wittgenstein>

On Mon, 2020-02-17 at 22:20 +0100, Christian Brauner wrote:
> On Mon, Feb 17, 2020 at 01:06:08PM -0800, James Bottomley wrote:
> > On Fri, 2020-02-14 at 19:35 +0100, Christian Brauner wrote:
> > [...]
> > > People not as familiar with user namespaces might not be aware
> > > that fsid mappings already exist. Right now, fsid mappings are
> > > always identical to id mappings. Specifically, the kernel will
> > > lookup fsuids in the uid mappings and fsgids in the gid mappings
> > > of the relevant user namespace.
> > 
> > This isn't actually entirely true: today we have the superblock
> > user namespace, which can be used for fsid remapping on filesystems
> > that support it (currently f2fs and fuse).  Since this is a single
> > shift,
> 
> Note that this states "the relevant" user namespace not the caller's
> user namespace. And the point is true even for such filesystems. fuse
> does call make_kuid(fc->user_ns, attr->uid) and hence looks up the
> mapping in the id mappings.. This would be replaced by make_kfsuid().
> 
> > how is it going to play with s_user_ns?  Do you have to understand
> > the superblock mapping to use this shift, or are we simply using
> > this to replace s_user_ns?
> 
> I'm not sure what you mean by understand the superblock mapping. The
> case is not different from the devpts patch in this series.

So since devpts wasn't originally a s_user_ns consumer, I assume you're
thinking that this patch series just replaces the whole of s_user_ns
for fuse and f2fs and we can remove it?

> Fuse needs to be changed to call make_kfsuid() since it is mountable
> inside user namespaces at which point everthing just works.

The fuse case is slightly more complicated because there are sound
reasons to run the daemon in a separate user namespace regardless of
where the end fuse mount is.

James


  reply	other threads:[~2020-02-17 22:35 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 18:35 [PATCH v2 00/28] user_namespace: introduce fsid mappings Christian Brauner
2020-02-14 18:35 ` [PATCH v2 01/28] user_namespace: introduce fsid mappings infrastructure Christian Brauner
2020-02-14 18:35 ` [PATCH v2 02/28] proc: add /proc/<pid>/fsuid_map Christian Brauner
2020-02-14 18:35 ` [PATCH v2 03/28] proc: add /proc/<pid>/fsgid_map Christian Brauner
2020-02-14 18:35 ` [PATCH v2 04/28] fsuidgid: add fsid mapping helpers Christian Brauner
2020-02-14 19:11   ` Jann Horn
2020-02-16 16:55     ` Christian Brauner
2020-02-14 18:35 ` [PATCH v2 05/28] proc: task_state(): use from_kfs{g,u}id_munged Christian Brauner
2020-02-14 18:35 ` [PATCH v2 06/28] cred: add kfs{g,u}id Christian Brauner
2020-02-14 18:35 ` [PATCH v2 07/28] sys: __sys_setfsuid(): handle fsid mappings Christian Brauner
2020-02-14 18:35 ` [PATCH v2 08/28] sys: __sys_setfsgid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 09/28] sys:__sys_setuid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 10/28] sys:__sys_setgid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 11/28] sys:__sys_setreuid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 12/28] sys:__sys_setregid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 13/28] sys:__sys_setresuid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 14/28] sys:__sys_setresgid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 15/28] fs: add is_userns_visible() helper Christian Brauner
2020-02-14 18:35 ` [PATCH v2 16/28] namei: may_{o_}create(): handle fsid mappings Christian Brauner
2020-02-14 18:35 ` [PATCH v2 17/28] inode: inode_owner_or_capable(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 18/28] capability: privileged_wrt_inode_uidgid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 19/28] stat: " Christian Brauner
2020-02-14 19:03   ` Tycho Andersen
2020-02-16 14:12     ` Christian Brauner
2020-02-14 18:35 ` [PATCH v2 20/28] open: " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 21/28] posix_acl: " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 22/28] attr: notify_change(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 23/28] commoncap: cap_bprm_set_creds(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 24/28] commoncap: cap_task_fix_setuid(): " Christian Brauner
2020-02-14 18:35 ` [PATCH v2 25/28] commoncap: handle fsid mappings with vfs caps Christian Brauner
2020-02-14 18:35 ` [PATCH v2 26/28] exec: bprm_fill_uid(): handle fsid mappings Christian Brauner
2020-02-14 18:35 ` [PATCH v2 27/28] ptrace: adapt ptrace_may_access() to always uses unmapped fsids Christian Brauner
2020-02-14 18:35 ` [PATCH v2 28/28] devpts: handle fsid mappings Christian Brauner
2020-02-16 15:55 ` [PATCH v2 00/28] user_namespace: introduce " Florian Weimer
2020-02-16 16:40   ` Christian Brauner
2020-02-17 21:06 ` James Bottomley
2020-02-17 21:20   ` Christian Brauner
2020-02-17 22:35     ` James Bottomley [this message]
2020-02-17 23:05       ` Christian Brauner
2020-02-17 21:11 ` James Bottomley
     [not found]   ` <CA+enf=vwd-dxzve87t7Mw1Z35RZqdLzVaKq=fZ4EGOpnES0f5w@mail.gmail.com>
2020-02-17 22:02     ` Stéphane Graber
2020-02-17 23:03     ` James Bottomley
2020-02-17 23:11       ` Stéphane Graber

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