Introspecting userns relationships to other namespaces?

Submitted by Andrey Vagin on July 8, 2016, 3 a.m.

Details

Message ID 20160708030055.GC10512@outlook.office365.com
State Rejected
Series "Introspecting userns relationships to other namespaces?"
Headers show

Commit Message

Andrey Vagin July 8, 2016, 3 a.m.
On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
> On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley wrote:
> > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages) wrote:
> > > On 7 July 2016 at 17:01, James Bottomley
> > > <James.Bottomley@hansenpartnership.com> wrote:
> > [Serge already answered the parenting issue]
> > > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote:
> > > > > Hm.  Probably best-effort based on the process hierarchy.  So 
> > > > > yeah you could probably get a tree into a state that would be 
> > > > > wrongly recreated. Create a new netns, bind mount it, exit;  Have 
> > > > > another task create a new user_ns, bind mount it, exit;  Third 
> > > > > task setns()s first to the new netns then to the new user_ns.  I 
> > > > > suspect criu will recreate that wrongly.
> > > > 
> > > > This is a bit pathological, and you have to be root to do it: so 
> > > > root can set up a nesting hierarchy, bind it and destroy the pids 
> > > > but I know of no current orchestration system which does this.
> > > > 
> > > > Actually, I have to back pedal a bit: the way I currently set up
> > > > architecture emulation containers does precisely this: I set up the
> > > > namespaces unprivileged with child mount namespaces, but then I ask
> > > > root to bind the userns and kill the process that created it so I 
> > > > have a permanent handle to enter the namespace by, so I suspect 
> > > > that when our current orchestration systems get more sophisticated, 
> > > > they might eventually want to do something like this as well.
> > > > 
> > > > In theory, we could get nsfs to show this information as an option
> > > > (just add a show_options entry to the superblock ops), but the 
> > > > problem is that although each namespace has a parent user_ns, 
> > > > there's no way to get it without digging in the namespace specific 
> > > > structure.  Probably we should restructure to move it into 
> > > > ns_common, then we could display it (and enforce all namespaces 
> > > > having owning user_ns) but it would be a
> > > 
> > > I'm missing something here. Is it not already the case that all
> > > namespaces have an owning user_ns?
> > 
> > Um, yes, I don't believe I said they don't.  The problem I thought you
> > were having is that there's no way of seeing what it is.
> > 
> > nsfs is the Namespace fileystem where bound namespaces appear to a cat
> > of /proc/self/mounts.  It can display any information that's in
> > ns_common (the common core of namespaces) but the owning user_ns
> > pointer currently isn't in this structure.  Every user namespace has a
> > pointer to it, but they're all privately embedded in the individual
> > namespace specific structures.  What I was proposing was that since
> > every current namespace has a pointer somewhere to the owning user
> > namespace, we could abstract this out into ns_common so it's now
> > accessible to be displayed by nsfs, probably as a mount option.
> 
> James, I am not sure that I understood you correctly. We have one
> file system for all namespace files, how we can show per-file properties
> in mount options. I think we can show all required information in
> fdinfo. We open a namespaces file (/proc/pid/ns/N) and then read
> /proc/pid/fdinfo/X for it.

Here is a proof-of-concept patch.

How it works:

In [1]: import os

In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)

In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
pos:	0
flags:	0100000
mnt_id:	2
userns: 4026531837

In [4]: print "/proc/self/ns/user -> %s" % os.readlink("/proc/self/ns/user")
/proc/self/ns/user -> user:[4026531837]

> 
> > 
> > James
> > 
> > 
> > _______________________________________________
> > CRIU mailing list
> > CRIU@openvz.org
> > https://lists.openvz.org/mailman/listinfo/criu
> _______________________________________________
> CRIU mailing list
> CRIU@openvz.org
> https://lists.openvz.org/mailman/listinfo/criu

Patch hide | download patch | download mbox

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 8f20d60..bfd5bde 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -8,8 +8,20 @@ 
 
 static struct vfsmount *nsfs_mnt;
 
+static void show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct dentry *dentry = f->f_path.dentry;
+	struct inode *inode = d_inode(dentry);
+	const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
+	struct ns_common *ns = inode->i_private;
+
+	if (ns_ops->show_fdinfo)
+		ns_ops->show_fdinfo(m, ns);
+}
+
 static const struct file_operations ns_file_operations = {
 	.llseek		= no_llseek,
+	.show_fdinfo	= show_fdinfo,
 };
 
 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index de0e771..fed276b 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -18,6 +18,7 @@  struct proc_ns_operations {
 	struct ns_common *(*get)(struct task_struct *task);
 	void (*put)(struct ns_common *ns);
 	int (*install)(struct nsproxy *nsproxy, struct ns_common *ns);
+	void (*show_fdinfo)(struct seq_file *m, struct ns_common *ns);
 };
 
 extern const struct proc_ns_operations netns_operations;
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index a65ba13..910b388 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -388,12 +388,20 @@  static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 	return 0;
 }
 
+static void pidns_fdinfo(struct seq_file *m, struct ns_common *ns)
+{
+	struct pid_namespace *pidns = to_pid_ns(ns);
+
+	seq_printf(m, "userns: %u\n", pidns->user_ns->ns.inum);
+}
+
 const struct proc_ns_operations pidns_operations = {
 	.name		= "pid",
 	.type		= CLONE_NEWPID,
 	.get		= pidns_get,
 	.put		= pidns_put,
 	.install	= pidns_install,
+	.show_fdinfo	= pidns_fdinfo,
 };
 
 static __init int pid_namespaces_init(void)

Comments

James Bottomley July 8, 2016, 3:26 a.m.
On Thu, 2016-07-07 at 20:00 -0700, Andrew Vagin wrote:
> On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
> > On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley wrote:
> > > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages)
> > > wrote:
> > > > On 7 July 2016 at 17:01, James Bottomley
> > > > <James.Bottomley@hansenpartnership.com> wrote:
> > > [Serge already answered the parenting issue]
> > > > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote:
> > > > > > Hm.  Probably best-effort based on the process hierarchy. 
> > > > > >  So 
> > > > > > yeah you could probably get a tree into a state that would
> > > > > > be 
> > > > > > wrongly recreated. Create a new netns, bind mount it, exit;
> > > > > >   Have 
> > > > > > another task create a new user_ns, bind mount it, exit; 
> > > > > >  Third 
> > > > > > task setns()s first to the new netns then to the new
> > > > > > user_ns.  I 
> > > > > > suspect criu will recreate that wrongly.
> > > > > 
> > > > > This is a bit pathological, and you have to be root to do it:
> > > > > so 
> > > > > root can set up a nesting hierarchy, bind it and destroy the
> > > > > pids 
> > > > > but I know of no current orchestration system which does
> > > > > this.
> > > > > 
> > > > > Actually, I have to back pedal a bit: the way I currently set
> > > > > up
> > > > > architecture emulation containers does precisely this: I set
> > > > > up the
> > > > > namespaces unprivileged with child mount namespaces, but then
> > > > > I ask
> > > > > root to bind the userns and kill the process that created it
> > > > > so I 
> > > > > have a permanent handle to enter the namespace by, so I
> > > > > suspect 
> > > > > that when our current orchestration systems get more
> > > > > sophisticated, 
> > > > > they might eventually want to do something like this as well.
> > > > > 
> > > > > In theory, we could get nsfs to show this information as an
> > > > > option
> > > > > (just add a show_options entry to the superblock ops), but
> > > > > the 
> > > > > problem is that although each namespace has a parent user_ns,
> > > > > there's no way to get it without digging in the namespace
> > > > > specific 
> > > > > structure.  Probably we should restructure to move it into 
> > > > > ns_common, then we could display it (and enforce all
> > > > > namespaces 
> > > > > having owning user_ns) but it would be a
> > > > 
> > > > I'm missing something here. Is it not already the case that all
> > > > namespaces have an owning user_ns?
> > > 
> > > Um, yes, I don't believe I said they don't.  The problem I
> > > thought you
> > > were having is that there's no way of seeing what it is.
> > > 
> > > nsfs is the Namespace fileystem where bound namespaces appear to
> > > a cat
> > > of /proc/self/mounts.  It can display any information that's in
> > > ns_common (the common core of namespaces) but the owning user_ns
> > > pointer currently isn't in this structure.  Every user namespace
> > > has a
> > > pointer to it, but they're all privately embedded in the
> > > individual
> > > namespace specific structures.  What I was proposing was that
> > > since
> > > every current namespace has a pointer somewhere to the owning
> > > user
> > > namespace, we could abstract this out into ns_common so it's now
> > > accessible to be displayed by nsfs, probably as a mount option.
> > 
> > James, I am not sure that I understood you correctly. We have one
> > file system for all namespace files, how we can show per-file
> > properties
> > in mount options. I think we can show all required information in
> > fdinfo. We open a namespaces file (/proc/pid/ns/N) and then read
> > /proc/pid/fdinfo/X for it.
> 
> Here is a proof-of-concept patch.
> 
> How it works:
> 
> In [1]: import os
> 
> In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)
> 
> In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
> pos:	0
> flags:	0100000
> mnt_id:	2
> userns: 4026531837
> 
> In [4]: print "/proc/self/ns/user -> %s" %
> os.readlink("/proc/self/ns/user")
> /proc/self/ns/user -> user:[4026531837]

can't you just do

readlink /proc/self/ns/user | sed 's/.*\[\(.*\)\]/\1/'

?

But what Michael was asking about was the parent user_ns of all the
other namespaces ... I don't think there's any way we can get that out
of any information in /proc/self/

James
Andrei Vagin July 8, 2016, 5:41 a.m.
On Thu, Jul 7, 2016 at 8:26 PM, James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
> On Thu, 2016-07-07 at 20:00 -0700, Andrew Vagin wrote:
>> On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
>> > On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley wrote:
>> > > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages)
>> > > wrote:
>> > > > On 7 July 2016 at 17:01, James Bottomley
>> > > > <James.Bottomley@hansenpartnership.com> wrote:
>> > > [Serge already answered the parenting issue]
>> > > > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote:
>> > > > > > Hm.  Probably best-effort based on the process hierarchy.
>> > > > > >  So
>> > > > > > yeah you could probably get a tree into a state that would
>> > > > > > be
>> > > > > > wrongly recreated. Create a new netns, bind mount it, exit;
>> > > > > >   Have
>> > > > > > another task create a new user_ns, bind mount it, exit;
>> > > > > >  Third
>> > > > > > task setns()s first to the new netns then to the new
>> > > > > > user_ns.  I
>> > > > > > suspect criu will recreate that wrongly.
>> > > > >
>> > > > > This is a bit pathological, and you have to be root to do it:
>> > > > > so
>> > > > > root can set up a nesting hierarchy, bind it and destroy the
>> > > > > pids
>> > > > > but I know of no current orchestration system which does
>> > > > > this.
>> > > > >
>> > > > > Actually, I have to back pedal a bit: the way I currently set
>> > > > > up
>> > > > > architecture emulation containers does precisely this: I set
>> > > > > up the
>> > > > > namespaces unprivileged with child mount namespaces, but then
>> > > > > I ask
>> > > > > root to bind the userns and kill the process that created it
>> > > > > so I
>> > > > > have a permanent handle to enter the namespace by, so I
>> > > > > suspect
>> > > > > that when our current orchestration systems get more
>> > > > > sophisticated,
>> > > > > they might eventually want to do something like this as well.
>> > > > >
>> > > > > In theory, we could get nsfs to show this information as an
>> > > > > option
>> > > > > (just add a show_options entry to the superblock ops), but
>> > > > > the
>> > > > > problem is that although each namespace has a parent user_ns,
>> > > > > there's no way to get it without digging in the namespace
>> > > > > specific
>> > > > > structure.  Probably we should restructure to move it into
>> > > > > ns_common, then we could display it (and enforce all
>> > > > > namespaces
>> > > > > having owning user_ns) but it would be a
>> > > >
>> > > > I'm missing something here. Is it not already the case that all
>> > > > namespaces have an owning user_ns?
>> > >
>> > > Um, yes, I don't believe I said they don't.  The problem I
>> > > thought you
>> > > were having is that there's no way of seeing what it is.
>> > >
>> > > nsfs is the Namespace fileystem where bound namespaces appear to
>> > > a cat
>> > > of /proc/self/mounts.  It can display any information that's in
>> > > ns_common (the common core of namespaces) but the owning user_ns
>> > > pointer currently isn't in this structure.  Every user namespace
>> > > has a
>> > > pointer to it, but they're all privately embedded in the
>> > > individual
>> > > namespace specific structures.  What I was proposing was that
>> > > since
>> > > every current namespace has a pointer somewhere to the owning
>> > > user
>> > > namespace, we could abstract this out into ns_common so it's now
>> > > accessible to be displayed by nsfs, probably as a mount option.
>> >
>> > James, I am not sure that I understood you correctly. We have one
>> > file system for all namespace files, how we can show per-file
>> > properties
>> > in mount options. I think we can show all required information in
>> > fdinfo. We open a namespaces file (/proc/pid/ns/N) and then read
>> > /proc/pid/fdinfo/X for it.
>>
>> Here is a proof-of-concept patch.
>>
>> How it works:
>>
>> In [1]: import os
>>
>> In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)
>>
>> In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
>> pos:  0
>> flags:        0100000
>> mnt_id:       2
>> userns: 4026531837
>>
>> In [4]: print "/proc/self/ns/user -> %s" %
>> os.readlink("/proc/self/ns/user")
>> /proc/self/ns/user -> user:[4026531837]
>
> can't you just do
>
> readlink /proc/self/ns/user | sed 's/.*\[\(.*\)\]/\1/'

We can get fdinfo for any ns file. I used /proc/self/ns/pid as an example.

Look at another example:

[root@fc22-vm ~]# cat /proc/self/mountinfo | grep pid_ns_file
115 38 0:3 pid:[4026532306] /tmp/pid_ns_file rw shared:67 - nsfs nsfs rw

In [4]: print open("/proc/self/fdinfo/5").read()
pos: 0
flags: 0100000
mnt_id: 115
userns: 4026532305


In [5]: os.readlink("/proc/self/ns/user")
Out[5]: 'user:[4026531837]'


>
> ?
>
> But what Michael was asking about was the parent user_ns of all the
> other namespaces ... I don't think there's any way we can get that out
> of any information in /proc/self/
>
> James
>
>
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers
Andrei Vagin July 8, 2016, 5:47 a.m.
On Thu, Jul 7, 2016 at 10:41 PM, Andrei Vagin <avagin@gmail.com> wrote:
> On Thu, Jul 7, 2016 at 8:26 PM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
>> On Thu, 2016-07-07 at 20:00 -0700, Andrew Vagin wrote:
>>> On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
>>> > On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley wrote:
>>> > > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages)
>>> > > wrote:
>>> > > > On 7 July 2016 at 17:01, James Bottomley
>>> > > > <James.Bottomley@hansenpartnership.com> wrote:
>>> > > [Serge already answered the parenting issue]
>>> > > > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote:
>>> > > > > > Hm.  Probably best-effort based on the process hierarchy.
>>> > > > > >  So
>>> > > > > > yeah you could probably get a tree into a state that would
>>> > > > > > be
>>> > > > > > wrongly recreated. Create a new netns, bind mount it, exit;
>>> > > > > >   Have
>>> > > > > > another task create a new user_ns, bind mount it, exit;
>>> > > > > >  Third
>>> > > > > > task setns()s first to the new netns then to the new
>>> > > > > > user_ns.  I
>>> > > > > > suspect criu will recreate that wrongly.
>>> > > > >
>>> > > > > This is a bit pathological, and you have to be root to do it:
>>> > > > > so
>>> > > > > root can set up a nesting hierarchy, bind it and destroy the
>>> > > > > pids
>>> > > > > but I know of no current orchestration system which does
>>> > > > > this.
>>> > > > >
>>> > > > > Actually, I have to back pedal a bit: the way I currently set
>>> > > > > up
>>> > > > > architecture emulation containers does precisely this: I set
>>> > > > > up the
>>> > > > > namespaces unprivileged with child mount namespaces, but then
>>> > > > > I ask
>>> > > > > root to bind the userns and kill the process that created it
>>> > > > > so I
>>> > > > > have a permanent handle to enter the namespace by, so I
>>> > > > > suspect
>>> > > > > that when our current orchestration systems get more
>>> > > > > sophisticated,
>>> > > > > they might eventually want to do something like this as well.
>>> > > > >
>>> > > > > In theory, we could get nsfs to show this information as an
>>> > > > > option
>>> > > > > (just add a show_options entry to the superblock ops), but
>>> > > > > the
>>> > > > > problem is that although each namespace has a parent user_ns,
>>> > > > > there's no way to get it without digging in the namespace
>>> > > > > specific
>>> > > > > structure.  Probably we should restructure to move it into
>>> > > > > ns_common, then we could display it (and enforce all
>>> > > > > namespaces
>>> > > > > having owning user_ns) but it would be a
>>> > > >
>>> > > > I'm missing something here. Is it not already the case that all
>>> > > > namespaces have an owning user_ns?
>>> > >
>>> > > Um, yes, I don't believe I said they don't.  The problem I
>>> > > thought you
>>> > > were having is that there's no way of seeing what it is.
>>> > >
>>> > > nsfs is the Namespace fileystem where bound namespaces appear to
>>> > > a cat
>>> > > of /proc/self/mounts.  It can display any information that's in
>>> > > ns_common (the common core of namespaces) but the owning user_ns
>>> > > pointer currently isn't in this structure.  Every user namespace
>>> > > has a
>>> > > pointer to it, but they're all privately embedded in the
>>> > > individual
>>> > > namespace specific structures.  What I was proposing was that
>>> > > since
>>> > > every current namespace has a pointer somewhere to the owning
>>> > > user
>>> > > namespace, we could abstract this out into ns_common so it's now
>>> > > accessible to be displayed by nsfs, probably as a mount option.
>>> >
>>> > James, I am not sure that I understood you correctly. We have one
>>> > file system for all namespace files, how we can show per-file
>>> > properties
>>> > in mount options. I think we can show all required information in
>>> > fdinfo. We open a namespaces file (/proc/pid/ns/N) and then read
>>> > /proc/pid/fdinfo/X for it.
>>>
>>> Here is a proof-of-concept patch.
>>>
>>> How it works:
>>>
>>> In [1]: import os
>>>
>>> In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)
>>>
>>> In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
>>> pos:  0
>>> flags:        0100000
>>> mnt_id:       2
>>> userns: 4026531837
>>>
>>> In [4]: print "/proc/self/ns/user -> %s" %
>>> os.readlink("/proc/self/ns/user")
>>> /proc/self/ns/user -> user:[4026531837]
>>
>> can't you just do
>>
>> readlink /proc/self/ns/user | sed 's/.*\[\(.*\)\]/\1/'
>
> We can get fdinfo for any ns file. I used /proc/self/ns/pid as an example.
>
> Look at another example:
>
> [root@fc22-vm ~]# cat /proc/self/mountinfo | grep pid_ns_file
> 115 38 0:3 pid:[4026532306] /tmp/pid_ns_file rw shared:67 - nsfs nsfs rw
>

Sorry, I forgot to say that fd is a file descriptor for /tmp/pid_ns_file

In [2]  : fd = os.open("/tmp/pid_ns_file", os.O_RDONLY)
In [3]  : fd
Out[4]: 5

> In [4]: print open("/proc/self/fdinfo/5").read()
> pos: 0
> flags: 0100000
> mnt_id: 115
> userns: 4026532305
>
>
> In [5]: os.readlink("/proc/self/ns/user")
> Out[5]: 'user:[4026531837]'
>
>
>>
>> ?
>>
>> But what Michael was asking about was the parent user_ns of all the
>> other namespaces ... I don't think there's any way we can get that out
>> of any information in /proc/self/
>>
>> James
>>
>>
>> _______________________________________________
>> Containers mailing list
>> Containers@lists.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/containers
James Bottomley July 8, 2016, 6:07 a.m.
On Thu, 2016-07-07 at 22:41 -0700, Andrei Vagin wrote:
> On Thu, Jul 7, 2016 at 8:26 PM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > On Thu, 2016-07-07 at 20:00 -0700, Andrew Vagin wrote:
> > > On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
> > > > On Thu, Jul 07, 2016 at 12:17:35PM -0700, James Bottomley
> > > > wrote:
> > > > > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man
> > > > > -pages)
> > > > > wrote:
> > > > > > On 7 July 2016 at 17:01, James Bottomley
> > > > > > <James.Bottomley@hansenpartnership.com> wrote:
> > > > > [Serge already answered the parenting issue]
> > > > > > > On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote:
> > > > > > > > Hm.  Probably best-effort based on the process
> > > > > > > > hierarchy.
> > > > > > > >  So
> > > > > > > > yeah you could probably get a tree into a state that
> > > > > > > > would
> > > > > > > > be
> > > > > > > > wrongly recreated. Create a new netns, bind mount it,
> > > > > > > > exit;
> > > > > > > >   Have
> > > > > > > > another task create a new user_ns, bind mount it, exit;
> > > > > > > >  Third
> > > > > > > > task setns()s first to the new netns then to the new
> > > > > > > > user_ns.  I
> > > > > > > > suspect criu will recreate that wrongly.
> > > > > > > 
> > > > > > > This is a bit pathological, and you have to be root to do
> > > > > > > it:
> > > > > > > so
> > > > > > > root can set up a nesting hierarchy, bind it and destroy
> > > > > > > the
> > > > > > > pids
> > > > > > > but I know of no current orchestration system which does
> > > > > > > this.
> > > > > > > 
> > > > > > > Actually, I have to back pedal a bit: the way I currently
> > > > > > > set
> > > > > > > up
> > > > > > > architecture emulation containers does precisely this: I
> > > > > > > set
> > > > > > > up the
> > > > > > > namespaces unprivileged with child mount namespaces, but
> > > > > > > then
> > > > > > > I ask
> > > > > > > root to bind the userns and kill the process that created
> > > > > > > it
> > > > > > > so I
> > > > > > > have a permanent handle to enter the namespace by, so I
> > > > > > > suspect
> > > > > > > that when our current orchestration systems get more
> > > > > > > sophisticated,
> > > > > > > they might eventually want to do something like this as
> > > > > > > well.
> > > > > > > 
> > > > > > > In theory, we could get nsfs to show this information as
> > > > > > > an
> > > > > > > option
> > > > > > > (just add a show_options entry to the superblock ops),
> > > > > > > but
> > > > > > > the
> > > > > > > problem is that although each namespace has a parent
> > > > > > > user_ns,
> > > > > > > there's no way to get it without digging in the namespace
> > > > > > > specific
> > > > > > > structure.  Probably we should restructure to move it
> > > > > > > into
> > > > > > > ns_common, then we could display it (and enforce all
> > > > > > > namespaces
> > > > > > > having owning user_ns) but it would be a
> > > > > > 
> > > > > > I'm missing something here. Is it not already the case that
> > > > > > all
> > > > > > namespaces have an owning user_ns?
> > > > > 
> > > > > Um, yes, I don't believe I said they don't.  The problem I
> > > > > thought you
> > > > > were having is that there's no way of seeing what it is.
> > > > > 
> > > > > nsfs is the Namespace fileystem where bound namespaces appear
> > > > > to
> > > > > a cat
> > > > > of /proc/self/mounts.  It can display any information that's
> > > > > in
> > > > > ns_common (the common core of namespaces) but the owning
> > > > > user_ns
> > > > > pointer currently isn't in this structure.  Every user
> > > > > namespace
> > > > > has a
> > > > > pointer to it, but they're all privately embedded in the
> > > > > individual
> > > > > namespace specific structures.  What I was proposing was that
> > > > > since
> > > > > every current namespace has a pointer somewhere to the owning
> > > > > user
> > > > > namespace, we could abstract this out into ns_common so it's
> > > > > now
> > > > > accessible to be displayed by nsfs, probably as a mount
> > > > > option.
> > > > 
> > > > James, I am not sure that I understood you correctly. We have
> > > > one
> > > > file system for all namespace files, how we can show per-file
> > > > properties
> > > > in mount options. I think we can show all required information
> > > > in
> > > > fdinfo. We open a namespaces file (/proc/pid/ns/N) and then
> > > > read
> > > > /proc/pid/fdinfo/X for it.
> > > 
> > > Here is a proof-of-concept patch.
> > > 
> > > How it works:
> > > 
> > > In [1]: import os
> > > 
> > > In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)
> > > 
> > > In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
> > > pos:  0
> > > flags:        0100000
> > > mnt_id:       2
> > > userns: 4026531837
> > > 
> > > In [4]: print "/proc/self/ns/user -> %s" %
> > > os.readlink("/proc/self/ns/user")
> > > /proc/self/ns/user -> user:[4026531837]
> > 
> > can't you just do
> > 
> > readlink /proc/self/ns/user | sed 's/.*\[\(.*\)\]/\1/'
> 
> We can get fdinfo for any ns file. I used /proc/self/ns/pid as an
> example.
> 
> Look at another example:
> 
> [root@fc22-vm ~]# cat /proc/self/mountinfo | grep pid_ns_file
> 115 38 0:3 pid:[4026532306] /tmp/pid_ns_file rw shared:67 - nsfs nsfs
> rw
> 
> In [4]: print open("/proc/self/fdinfo/5").read()
> pos: 0
> flags: 0100000
> mnt_id: 115
> userns: 4026532305

OK, I'm missing where this is coming from specifically.  There would
have to be a show_fdinfo() somewhere that did this and I'm not finding
it in linux-next.

James
Andrey Vagin July 8, 2016, 6:54 a.m.
On Thu, Jul 07, 2016 at 10:26:50PM -0700, W. Trevor King wrote:
> On Thu, Jul 07, 2016 at 08:26:47PM -0700, James Bottomley wrote:
> > On Thu, 2016-07-07 at 20:00 -0700, Andrew Vagin wrote:
> > > On Thu, Jul 07, 2016 at 07:16:18PM -0700, Andrew Vagin wrote:
> > > > I think we can show all required information in fdinfo. We open
> > > > a namespaces file (/proc/pid/ns/N) and then read
> > > > /proc/pid/fdinfo/X for it.
> > > 
> > > Here is a proof-of-concept patch.
> > > …
> > > In [2]: fd = os.open("/proc/self/ns/pid", os.O_RDONLY)
> > > 
> > > In [3]: print open("/proc/self/fdinfo/%d" % fd).read()
> > > pos:	0
> > > flags:	0100000
> > > mnt_id:	2
> > > userns: 4026531837
> > > 
> > > In [4]: print "/proc/self/ns/user -> %s" %
> > > os.readlink("/proc/self/ns/user")
> > > /proc/self/ns/user -> user:[4026531837]
> > 
> > can't you just do
> > 
> > readlink /proc/self/ns/user | sed 's/.*\[\(.*\)\]/\1/'
> 
> With Andrew's fdinfo approach you know the user namespace owning
> /proc/self/ns/pid is 4026531837.  That happens to be
> /proc/self/ns/user in this case, but doesn't have to be in general.
> 
> > But what Michael was asking about was the parent user_ns of all the
> > other namespaces ... I don't think there's any way we can get that
> > out of any information in /proc/self/
> 
> If fdinfo only shows immediate parents, you'd need to walk the tree to
> get back to the root.  And at each layer of the PID namespace tree
> there will be another user-namespace parent branching off).  With a
> tree like:
> 
>   Namespace         | Parent       | Owning userns
>  -------------------+--------------+-------------------
>   Root userns       | -            | -
>   Root PID ns       | -            | Root userns
>   Child userns      | Root usens   | Root userns
>   Child PID ns      | Root PID ns  | Root userns
>   Grandchild userns | Child userns | Child userns
>   Grandchild PID ns | Child PID ns | Grandchild userns
> 
> Walking from the granchild PID namespace would give you:
> 
>   Grandchild PID ns
>   |-- Child PID ns
>   |   |-- Root PID ns
>   |   `-- Root userns 
>   `-- Granchild userns
>       `-- Child userns
>           `-- Root userns
> 
> If you only put one level in fdinfo, you're stuck if one of the
> namespaces involved has neither bind mounts nor a PID to give you
> handle on it [1].  And if you want to put that whole ancestor tree in
> fdinfo, you have to come up with some way to handle the two-parent
> branching.

I think it's a bad idea to draw a tree in fdinfo. Why do we want to know
this hierarchy? Probably we will want to access these namespaces (setns),
in this case we need to have a way to open them.

Maybe we need to extend functionality of the nsfs filesystem
(somethink like /proc/PID for namespaces)?

> 
> I'm also not sure how exposing nsfs information [2] would handle
> namespaces that had neither a surviving bind mount nor a direct
> process.
> 
> If all the information is available (possible after a mechanical patch
> [3] makes it more accessible), then it seems easier to put it in a
> separate /proc or /sys file.  There was a stab at this for PID
> namespaces in [4] (the same series that landed NStgid, etc.) with
> additional background and alternative approaches in [5].  There were
> problems with that patch (and it was trying to do more by also listing
> a process's ID in each PID namespace), but the “let's put the whole
> tree in a new file” approach seems sound to me.
> 
> Cheers,
> Trevor
> 
> [1]: http://thread.gmane.org/gmane.linux.kernel.containers/30456/focus=20536
>      Subject: Re: Introspecting userns relationships to other namespaces?
>      Date: Thu, 7 Jul 2016 13:24:42 -0500
>      Message-ID: <20160707182442.GA6402@mail.hallyn.com>
> [2]: http://thread.gmane.org/gmane.linux.kernel.containers/30456/focus=30499
>      Subject: Re: [CRIU] Introspecting userns relationships to other namespaces?
>      Date: Thu, 07 Jul 2016 20:20:05 -0700
>      Message-ID: <1467948005.2322.84.camel@HansenPartnership.com>
> [3]: http://thread.gmane.org/gmane.linux.kernel.containers/30456/focus=20537
>      Subject: Re: Introspecting userns relationships to other namespaces?
>      Message-ID: <1467903712.2347.16.camel@HansenPartnership.com>
>      Date: Thu, 07 Jul 2016 08:01:52 -0700
> [4]: http://thread.gmane.org/gmane.linux.kernel.containers/28925/focus=28928
>      Subject: [resend][PATCH v9 1/3] procfs: show hierarchy of pid namespace
>      Date: Tue, 23 Dec 2014 18:20:37 +0800
>      Message-ID: <1419330039-29207-2-git-send-email-chenhanxiao@cn.fujitsu.com>
> [5]: http://thread.gmane.org/gmane.linux.kernel.containers/28105
>      Subject: [RFC]Pid conversion between pid namespace
>      Date: Thu, 3 Jul 2014 12:18:33 +0000
>      Message-ID: <5871495633F38949900D2BF2DC04883E55C374@G08CNEXMBPEKD02.g08.fujitsu.local>
> 
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