[PATCHv2] zram: restrict add/remove attributes to root only

[PATCHv2] zram: restrict add/remove attributes to root only

[Sergey Senozhatsky]

zram hot_add sysfs attribute is a very 'special' attribute - reading
from it creates a new uninitialized zram device. This file, by a mistake,
can be read by a 'normal' user at the moment, while only root must be
able to create a new zram device, therefore hot_add attribute must have
S_IRUSR mode, not S_IRUGO.

Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
Reported-by: Steven Allen <steven@stebalien.com>
Cc: <stable@vger.kernel.org>    [4.2+]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5163c8f..3a0576f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1413,9 +1413,16 @@ static ssize_t hot_remove_store(struct class *class,
 	return ret ? ret : count;
 }
 
+/*
+ * NOTE: hot_add attribute is not the usual read-only sysfs
+ * attribute. In a sence that reading from this file does alter
+ * the state of your system -- it creates a new un-initialized
+ * zram device and returns back this device's device_id (or an
+ * error code if it fails to create a new device).
+ */
 static struct class_attribute zram_control_class_attrs[] = {
-	__ATTR_RO(hot_add),
-	__ATTR_WO(hot_remove),
+	__ATTR(hot_add, 0400, hot_add_show, NULL),
+	__ATTR(hot_remove, 0200, NULL, hot_remove_store),
 	__ATTR_NULL,
 };
 
-- 
2.10.2

Re: [PATCHv2] zram: restrict add/remove attributes to root only

[Greg KH]

On Sun, Dec 04, 2016 at 09:44:13PM +0900, Sergey Senozhatsky wrote:
> zram hot_add sysfs attribute is a very 'special' attribute - reading
> from it creates a new uninitialized zram device. This file, by a mistake,
> can be read by a 'normal' user at the moment, while only root must be
> able to create a new zram device, therefore hot_add attribute must have
> S_IRUSR mode, not S_IRUGO.
> 
> Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
> Reported-by: Steven Allen <steven@stebalien.com>
> Cc: <stable@vger.kernel.org>    [4.2+]
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>  drivers/block/zram/zram_drv.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 5163c8f..3a0576f 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1413,9 +1413,16 @@ static ssize_t hot_remove_store(struct class *class,
>  	return ret ? ret : count;
>  }
>  
> +/*
> + * NOTE: hot_add attribute is not the usual read-only sysfs
> + * attribute. In a sence that reading from this file does alter
> + * the state of your system -- it creates a new un-initialized
> + * zram device and returns back this device's device_id (or an
> + * error code if it fails to create a new device).
> + */
>  static struct class_attribute zram_control_class_attrs[] = {
> -	__ATTR_RO(hot_add),
> -	__ATTR_WO(hot_remove),
> +	__ATTR(hot_add, 0400, hot_add_show, NULL),
> +	__ATTR(hot_remove, 0200, NULL, hot_remove_store),

You can leave hot_remove as __ATTR_WO(), right?  Please do so if at all
possible.

thanks,

greg k-h

Re: [PATCHv2] zram: restrict add/remove attributes to root only

[Sergey Senozhatsky]

On (12/05/16 13:57), Greg KH wrote:
> > +/*
> > + * NOTE: hot_add attribute is not the usual read-only sysfs
> > + * attribute. In a sence that reading from this file does alter
> > + * the state of your system -- it creates a new un-initialized
> > + * zram device and returns back this device's device_id (or an
> > + * error code if it fails to create a new device).
> > + */
> >  static struct class_attribute zram_control_class_attrs[] = {
> > -	__ATTR_RO(hot_add),
> > -	__ATTR_WO(hot_remove),
> > +	__ATTR(hot_add, 0400, hot_add_show, NULL),
> > +	__ATTR(hot_remove, 0200, NULL, hot_remove_store),
> 
> You can leave hot_remove as __ATTR_WO(), right?

yes. I changed it deliberately.

> Please do so if at all possible.

ok.

	-ss

[PATCHv3] zram: restrict add/remove attributes to root only

[Sergey Senozhatsky]

zram hot_add sysfs attribute is a very 'special' attribute - reading
from it creates a new uninitialized zram device. This file, by a mistake,
can be read by a 'normal' user at the moment, while only root must be
able to create a new zram device, therefore hot_add attribute must have
S_IRUSR mode, not S_IRUGO.

Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
Reported-by: Steven Allen <steven@stebalien.com>
Cc: <stable@vger.kernel.org>    [4.2+]
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 5163c8f..cc8d0b5 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1413,8 +1413,15 @@ static ssize_t hot_remove_store(struct class *class,
 	return ret ? ret : count;
 }
 
+/*
+ * NOTE: hot_add attribute is not the usual read-only sysfs
+ * attribute. In a sence that reading from this file does alter
+ * the state of your system -- it creates a new un-initialized
+ * zram device and returns back this device's device_id (or an
+ * error code if it fails to create a new device).
+ */
 static struct class_attribute zram_control_class_attrs[] = {
-	__ATTR_RO(hot_add),
+	__ATTR(hot_add, 0400, hot_add_show, NULL),
 	__ATTR_WO(hot_remove),
 	__ATTR_NULL,
 };
-- 
2.10.2

Re: [PATCHv3] zram: restrict add/remove attributes to root only

[Greg KH]

On Tue, Dec 06, 2016 at 12:58:45AM +0900, Sergey Senozhatsky wrote:
> zram hot_add sysfs attribute is a very 'special' attribute - reading
> from it creates a new uninitialized zram device. This file, by a mistake,
> can be read by a 'normal' user at the moment, while only root must be
> able to create a new zram device, therefore hot_add attribute must have
> S_IRUSR mode, not S_IRUGO.
> 
> Fixes: 6566d1a32bf72 ("zram: add dynamic device add/remove functionality")
> Reported-by: Steven Allen <steven@stebalien.com>
> Cc: <stable@vger.kernel.org>    [4.2+]
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>