Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2016-01-27 Thread Ian Campbell 
On Tue, 2016-01-26 at 17:15 +, Stefano Stabellini wrote:
> It is sufficient to create an empty save file, as returned by
> libxl__device_model_savefile, with the right owner, at domain creation
> time. Something like below:
> 
> diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> index a088d71..f908422 100644
> --- a/tools/libxl/libxl_dm.c
> +++ b/tools/libxl/libxl_dm.c
> @@ -1285,6 +1285,12 @@ end_search:
>  if (user != NULL && strcmp(user, "root")) {
>  flexarray_append(dm_args, "-runas");
>  flexarray_append(dm_args, user);
> +
> +const char *filename = libxl__device_model_savefile(gc, 
> guest_domid);
> +int fd = open(filename, O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 
> 0600);
> +struct passwd *pw = getpwnam(user);
> +fchown(fd, pw->pw_uid, pw->pw_gid);
> +close(fd);
>  }
>  }
>  flexarray_append(dm_args, NULL);
> 
> This is another thing that would be easier to fix after Ian's privsep
> series, because we'll have a better place for this code.

Right.

In the meantime I think we should update at least docs/misc/qemu-
deprivilege.txt and probably docs/man/xl.cfg.pod.5:device_model_user to
mention the shortcomings of using these options if they are going to break
core functionality such as migration.

Would you knock up a patch please?

At the same time, I wonder if docs/misc/qemu-deprivilege.txt ought to move
to docs/features/ ?

Ian.

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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2016-01-26 Thread Ian Campbell 
On Tue, 2016-01-26 at 00:00 +, Andrew Cooper wrote:
> On 25/01/2016 20:36, Konrad Rzeszutek Wilk wrote:
> > On Wed, Dec 30, 2015 at 11:00:52AM +, Andrew Cooper wrote:
> > > On 30/12/2015 05:25, Wen Congyang wrote:
> > > > On 12/30/2015 12:11 PM, Doug Goldstein wrote:
> > > > > On 12/29/15 8:39 PM, Wen Congyang wrote:
> > > > > > We may use non-root user to run qemu, and the qemu needs to
> > > > > > write
> > > > > > save file to /var/lib/xen. So we should allow all user to
> > > > > > create
> > > > > > a file under the directory /var/lib/xen
> > > > > > 
> > > > > > Signed-off-by: Wen Congyang 
> > > > > > ---
> > > > > >  tools/Makefile | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/tools/Makefile b/tools/Makefile
> > > > > > index 820ca40..402b417 100644
> > > > > > --- a/tools/Makefile
> > > > > > +++ b/tools/Makefile
> > > > > > @@ -60,7 +60,7 @@ build all: subdirs-all
> > > > > >  install: subdirs-install
> > > > > >     $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
> > > > > >     $(INSTALL_DIR) $(DESTDIR)/var/log/xen
> > > > > > -   $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
> > > > > > +   $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
> > > > > >  .PHONY: uninstall
> > > > > >  uninstall: D=$(DESTDIR)
> > > > > > 
> > > > > I could be wrong but this doesn't seem like something that you'd
> > > > > want to
> > > > > do given what's stored in there. Could you do something with
> > > > > permissions
> > > > > on sub-directories to achieve what you need?
> > > > > 
> > > > The save file's path is:
> > > > #define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /*
> > > > .$domid */
> > > > 
> > > > So all user must have write permission on the directory
> > > > /var/lib/xen/, otherwise,
> > > > the migration will fail.
> > > For now, I would avoid running qemu as a non-root user.  It doesn't
> > > gain you
> > > any meaninful security at present (at the expense of a warning which
> > > can't
> > > be turned off).
> > > 
> > > As to this bug, marking the directory 0777 is not an option, as save
> > > records
> > > necessarily contain sensitive data.
> > > 
> > > Longterm, (and already identified in one of the threads in the past),
> > > the
> > > best course of action is to switch away from having files, and
> > > passing file
> > > descriptors instead.  This is more flexible (currently libxl can't
> > > function
> > > on a read-only root filesystem), and would allow a privileged entity
> > > to open
> > > the file descriptor and pass it to a non-privileged entity to
> > > use.  This
> > > allows the non-privileged entity to function, and maintains security.
> > Wen,
> > 
> > Could you mention the use case for wanting to write files there?
> > Looking
> > at the patches you had sent for COLO and Remus they use an file
> > descriptor - so
> > what is the use-case here?
> 
> This is a bug in existing code.  It is not a COLO specific issue.
> 
> The current protocol for live migration requires Qemu to write its save
> file here.
> 
> Until this issue is resolved, live migration is inoperable with Qemu
> running as a non-root user.

Stefano, is this already on your list of issues to address?

In any case creating a world writeable directory is clearly a non-starter.
We might need the toolstack to create a directory with suitable permissions
until we can rework things to work with fds only.

Ian.


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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2016-01-26 Thread Stefano Stabellini 
On Tue, 26 Jan 2016, Ian Campbell wrote:
> On Tue, 2016-01-26 at 00:00 +, Andrew Cooper wrote:
> > On 25/01/2016 20:36, Konrad Rzeszutek Wilk wrote:
> > > On Wed, Dec 30, 2015 at 11:00:52AM +, Andrew Cooper wrote:
> > > > On 30/12/2015 05:25, Wen Congyang wrote:
> > > > > On 12/30/2015 12:11 PM, Doug Goldstein wrote:
> > > > > > On 12/29/15 8:39 PM, Wen Congyang wrote:
> > > > > > > We may use non-root user to run qemu, and the qemu needs to
> > > > > > > write
> > > > > > > save file to /var/lib/xen. So we should allow all user to
> > > > > > > create
> > > > > > > a file under the directory /var/lib/xen
> > > > > > >
> > > > > > > Signed-off-by: Wen Congyang 
> > > > > > > ---
> > > > > > >  tools/Makefile | 2 +-
> > > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > >
> > > > > > > diff --git a/tools/Makefile b/tools/Makefile
> > > > > > > index 820ca40..402b417 100644
> > > > > > > --- a/tools/Makefile
> > > > > > > +++ b/tools/Makefile
> > > > > > > @@ -60,7 +60,7 @@ build all: subdirs-all
> > > > > > >  install: subdirs-install
> > > > > > >   $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
> > > > > > >   $(INSTALL_DIR) $(DESTDIR)/var/log/xen
> > > > > > > - $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
> > > > > > > + $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
> > > > > > >  .PHONY: uninstall
> > > > > > >  uninstall: D=$(DESTDIR)
> > > > > > >
> > > > > > I could be wrong but this doesn't seem like something that you'd
> > > > > > want to
> > > > > > do given what's stored in there. Could you do something with
> > > > > > permissions
> > > > > > on sub-directories to achieve what you need?
> > > > > >
> > > > > The save file's path is:
> > > > > #define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /*
> > > > > .$domid */
> > > > >
> > > > > So all user must have write permission on the directory
> > > > > /var/lib/xen/, otherwise,
> > > > > the migration will fail.
> > > > For now, I would avoid running qemu as a non-root user.  It doesn't
> > > > gain you
> > > > any meaninful security at present (at the expense of a warning which
> > > > can't
> > > > be turned off).
> > > >
> > > > As to this bug, marking the directory 0777 is not an option, as save
> > > > records
> > > > necessarily contain sensitive data.
> > > >
> > > > Longterm, (and already identified in one of the threads in the past),
> > > > the
> > > > best course of action is to switch away from having files, and
> > > > passing file
> > > > descriptors instead.  This is more flexible (currently libxl can't
> > > > function
> > > > on a read-only root filesystem), and would allow a privileged entity
> > > > to open
> > > > the file descriptor and pass it to a non-privileged entity to
> > > > use.  This
> > > > allows the non-privileged entity to function, and maintains security.
> > > Wen,
> > >
> > > Could you mention the use case for wanting to write files there?
> > > Looking
> > > at the patches you had sent for COLO and Remus they use an file
> > > descriptor - so
> > > what is the use-case here?
> >
> > This is a bug in existing code.  It is not a COLO specific issue.
> >
> > The current protocol for live migration requires Qemu to write its save
> > file here.
> >
> > Until this issue is resolved, live migration is inoperable with Qemu
> > running as a non-root user.
>
> Stefano, is this already on your list of issues to address?
>
> In any case creating a world writeable directory is clearly a non-starter.
> We might need the toolstack to create a directory with suitable permissions
> until we can rework things to work with fds only.

It is sufficient to create an empty save file, as returned by
libxl__device_model_savefile, with the right owner, at domain creation
time. Something like below:

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index a088d71..f908422 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -1285,6 +1285,12 @@ end_search:
 if (user != NULL && strcmp(user, "root")) {
 flexarray_append(dm_args, "-runas");
 flexarray_append(dm_args, user);
+
+const char *filename = libxl__device_model_savefile(gc, 
guest_domid);
+int fd = open(filename, O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 
0600);
+struct passwd *pw = getpwnam(user);
+fchown(fd, pw->pw_uid, pw->pw_gid);
+close(fd);
 }
 }
 flexarray_append(dm_args, NULL);

This is another thing that would be easier to fix after Ian's privsep
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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2016-01-25 Thread Konrad Rzeszutek Wilk 
On Wed, Dec 30, 2015 at 11:00:52AM +, Andrew Cooper wrote:
> On 30/12/2015 05:25, Wen Congyang wrote:
> >On 12/30/2015 12:11 PM, Doug Goldstein wrote:
> >>On 12/29/15 8:39 PM, Wen Congyang wrote:
> >>>We may use non-root user to run qemu, and the qemu needs to write
> >>>save file to /var/lib/xen. So we should allow all user to create
> >>>a file under the directory /var/lib/xen
> >>>
> >>>Signed-off-by: Wen Congyang 
> >>>---
> >>>  tools/Makefile | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>>diff --git a/tools/Makefile b/tools/Makefile
> >>>index 820ca40..402b417 100644
> >>>--- a/tools/Makefile
> >>>+++ b/tools/Makefile
> >>>@@ -60,7 +60,7 @@ build all: subdirs-all
> >>>  install: subdirs-install
> >>>   $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
> >>>   $(INSTALL_DIR) $(DESTDIR)/var/log/xen
> >>>-  $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
> >>>+  $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
> >>>  .PHONY: uninstall
> >>>  uninstall: D=$(DESTDIR)
> >>>
> >>I could be wrong but this doesn't seem like something that you'd want to
> >>do given what's stored in there. Could you do something with permissions
> >>on sub-directories to achieve what you need?
> >>
> >The save file's path is:
> >#define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /* .$domid */
> >
> >So all user must have write permission on the directory /var/lib/xen/, 
> >otherwise,
> >the migration will fail.
> 
> For now, I would avoid running qemu as a non-root user.  It doesn't gain you
> any meaninful security at present (at the expense of a warning which can't
> be turned off).
> 
> As to this bug, marking the directory 0777 is not an option, as save records
> necessarily contain sensitive data.
> 
> Longterm, (and already identified in one of the threads in the past), the
> best course of action is to switch away from having files, and passing file
> descriptors instead.  This is more flexible (currently libxl can't function
> on a read-only root filesystem), and would allow a privileged entity to open
> the file descriptor and pass it to a non-privileged entity to use.  This
> allows the non-privileged entity to function, and maintains security.

Wen,

Could you mention the use case for wanting to write files there? Looking
at the patches you had sent for COLO and Remus they use an file descriptor - so
what is the use-case here?

Thanks!
> 
> ~Andrew
> 
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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2016-01-25 Thread Andrew Cooper 
On 25/01/2016 20:36, Konrad Rzeszutek Wilk wrote:
> On Wed, Dec 30, 2015 at 11:00:52AM +, Andrew Cooper wrote:
>> On 30/12/2015 05:25, Wen Congyang wrote:
>>> On 12/30/2015 12:11 PM, Doug Goldstein wrote:
 On 12/29/15 8:39 PM, Wen Congyang wrote:
> We may use non-root user to run qemu, and the qemu needs to write
> save file to /var/lib/xen. So we should allow all user to create
> a file under the directory /var/lib/xen
>
> Signed-off-by: Wen Congyang 
> ---
>  tools/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/Makefile b/tools/Makefile
> index 820ca40..402b417 100644
> --- a/tools/Makefile
> +++ b/tools/Makefile
> @@ -60,7 +60,7 @@ build all: subdirs-all
>  install: subdirs-install
>   $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
>   $(INSTALL_DIR) $(DESTDIR)/var/log/xen
> - $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
> + $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
>  .PHONY: uninstall
>  uninstall: D=$(DESTDIR)
>
 I could be wrong but this doesn't seem like something that you'd want to
 do given what's stored in there. Could you do something with permissions
 on sub-directories to achieve what you need?

>>> The save file's path is:
>>> #define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /* .$domid */
>>>
>>> So all user must have write permission on the directory /var/lib/xen/, 
>>> otherwise,
>>> the migration will fail.
>> For now, I would avoid running qemu as a non-root user.  It doesn't gain you
>> any meaninful security at present (at the expense of a warning which can't
>> be turned off).
>>
>> As to this bug, marking the directory 0777 is not an option, as save records
>> necessarily contain sensitive data.
>>
>> Longterm, (and already identified in one of the threads in the past), the
>> best course of action is to switch away from having files, and passing file
>> descriptors instead.  This is more flexible (currently libxl can't function
>> on a read-only root filesystem), and would allow a privileged entity to open
>> the file descriptor and pass it to a non-privileged entity to use.  This
>> allows the non-privileged entity to function, and maintains security.
> Wen,
>
> Could you mention the use case for wanting to write files there? Looking
> at the patches you had sent for COLO and Remus they use an file descriptor - 
> so
> what is the use-case here?

This is a bug in existing code.  It is not a COLO specific issue.

The current protocol for live migration requires Qemu to write its save
file here.

Until this issue is resolved, live migration is inoperable with Qemu
running as a non-root user.

~Andrew

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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2015-12-30 Thread Andrew Cooper 

On 30/12/2015 05:25, Wen Congyang wrote:

On 12/30/2015 12:11 PM, Doug Goldstein wrote:

On 12/29/15 8:39 PM, Wen Congyang wrote:

We may use non-root user to run qemu, and the qemu needs to write
save file to /var/lib/xen. So we should allow all user to create
a file under the directory /var/lib/xen

Signed-off-by: Wen Congyang 
---
  tools/Makefile | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/Makefile b/tools/Makefile
index 820ca40..402b417 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -60,7 +60,7 @@ build all: subdirs-all
  install: subdirs-install
$(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
$(INSTALL_DIR) $(DESTDIR)/var/log/xen
-   $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
+   $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
  
  .PHONY: uninstall

  uninstall: D=$(DESTDIR)


I could be wrong but this doesn't seem like something that you'd want to
do given what's stored in there. Could you do something with permissions
on sub-directories to achieve what you need?


The save file's path is:
#define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /* .$domid */

So all user must have write permission on the directory /var/lib/xen/, 
otherwise,
the migration will fail.


For now, I would avoid running qemu as a non-root user.  It doesn't gain 
you any meaninful security at present (at the expense of a warning which 
can't be turned off).


As to this bug, marking the directory 0777 is not an option, as save 
records necessarily contain sensitive data.


Longterm, (and already identified in one of the threads in the past), 
the best course of action is to switch away from having files, and 
passing file descriptors instead.  This is more flexible (currently 
libxl can't function on a read-only root filesystem), and would allow a 
privileged entity to open the file descriptor and pass it to a 
non-privileged entity to use.  This allows the non-privileged entity to 
function, and maintains security.


~Andrew

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[Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2015-12-29 Thread Wen Congyang 
We may use non-root user to run qemu, and the qemu needs to write
save file to /var/lib/xen. So we should allow all user to create
a file under the directory /var/lib/xen

Signed-off-by: Wen Congyang 
---
 tools/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/Makefile b/tools/Makefile
index 820ca40..402b417 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -60,7 +60,7 @@ build all: subdirs-all
 install: subdirs-install
$(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
$(INSTALL_DIR) $(DESTDIR)/var/log/xen
-   $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
+   $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
 
 .PHONY: uninstall
 uninstall: D=$(DESTDIR)
-- 
2.5.0




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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2015-12-29 Thread Wen Congyang 
On 12/30/2015 12:11 PM, Doug Goldstein wrote:
> On 12/29/15 8:39 PM, Wen Congyang wrote:
>> We may use non-root user to run qemu, and the qemu needs to write
>> save file to /var/lib/xen. So we should allow all user to create
>> a file under the directory /var/lib/xen
>>
>> Signed-off-by: Wen Congyang 
>> ---
>>  tools/Makefile | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/Makefile b/tools/Makefile
>> index 820ca40..402b417 100644
>> --- a/tools/Makefile
>> +++ b/tools/Makefile
>> @@ -60,7 +60,7 @@ build all: subdirs-all
>>  install: subdirs-install
>>  $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
>>  $(INSTALL_DIR) $(DESTDIR)/var/log/xen
>> -$(INSTALL_DIR) $(DESTDIR)/var/lib/xen
>> +$(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
>>  
>>  .PHONY: uninstall
>>  uninstall: D=$(DESTDIR)
>>
> 
> I could be wrong but this doesn't seem like something that you'd want to
> do given what's stored in there. Could you do something with permissions
> on sub-directories to achieve what you need?
> 

The save file's path is:
#define LIBXL_DEVICE_MODEL_SAVE_FILE "/var/lib/xen/qemu-save" /* .$domid */

So all user must have write permission on the directory /var/lib/xen/, 
otherwise,
the migration will fail.

Thanks
Wen Congyang




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Re: [Xen-devel] [PATCH 5/5] Allow all user to create a file under the directory /var/lib/xen

2015-12-29 Thread Doug Goldstein 
On 12/29/15 8:39 PM, Wen Congyang wrote:
> We may use non-root user to run qemu, and the qemu needs to write
> save file to /var/lib/xen. So we should allow all user to create
> a file under the directory /var/lib/xen
> 
> Signed-off-by: Wen Congyang 
> ---
>  tools/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/Makefile b/tools/Makefile
> index 820ca40..402b417 100644
> --- a/tools/Makefile
> +++ b/tools/Makefile
> @@ -60,7 +60,7 @@ build all: subdirs-all
>  install: subdirs-install
>   $(INSTALL_DIR) -m 700 $(DESTDIR)$(XEN_DUMP_DIR)
>   $(INSTALL_DIR) $(DESTDIR)/var/log/xen
> - $(INSTALL_DIR) $(DESTDIR)/var/lib/xen
> + $(INSTALL_DIR) -m 777 $(DESTDIR)/var/lib/xen
>  
>  .PHONY: uninstall
>  uninstall: D=$(DESTDIR)
> 

I could be wrong but this doesn't seem like something that you'd want to
do given what's stored in there. Could you do something with permissions
on sub-directories to achieve what you need?

-- 
Doug Goldstein



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