rbd: require global CAP_SYS_ADMIN for mapping and unmapping

It turns out that currently we rely only on sysfs attribute
permissions:

  $ ll /sys/bus/rbd/{add*,remove*}
  --w------- 1 root root 4096 Sep  3 20:37 /sys/bus/rbd/add
  --w------- 1 root root 4096 Sep  3 20:37 /sys/bus/rbd/add_single_major
  --w------- 1 root root 4096 Sep  3 20:37 /sys/bus/rbd/remove
  --w------- 1 root root 4096 Sep  3 20:38 /sys/bus/rbd/remove_single_major

This means that images can be mapped and unmapped (i.e. block devices
can be created and deleted) by a UID 0 process even after it drops all
privileges or by any process with CAP_DAC_OVERRIDE in its user namespace
as long as UID 0 is mapped into that user namespace.

Be consistent with other virtual block devices (loop, nbd, dm, md, etc)
and require CAP_SYS_ADMIN in the initial user namespace for mapping and
unmapping, and also for dumping the configuration string and refreshing
the image header.

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 011539039693210f1ce5d413cef0eab10cbe3d76..e77eaab5cf23ed1192be0b9bbebb32fb238a136d 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5120,6 +5120,9 @@ static ssize_t rbd_config_info_show(struct device *dev,
 {
        struct rbd_device *rbd_dev = dev_to_rbd_dev(dev);
 
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
        return sprintf(buf, "%s\n", rbd_dev->config_info);
 }
 
@@ -5231,6 +5234,9 @@ static ssize_t rbd_image_refresh(struct device *dev,
        struct rbd_device *rbd_dev = dev_to_rbd_dev(dev);
        int ret;
 
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
        ret = rbd_dev_refresh(rbd_dev);
        if (ret)
                return ret;
@@ -7059,6 +7065,9 @@ static ssize_t do_rbd_add(struct bus_type *bus,
        struct rbd_client *rbdc;
        int rc;
 
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
        if (!try_module_get(THIS_MODULE))
                return -ENODEV;
 
@@ -7209,6 +7218,9 @@ static ssize_t do_rbd_remove(struct bus_type *bus,
        bool force = false;
        int ret;
 
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
        dev_id = -1;
        opt_buf[0] = '\0';
        sscanf(buf, "%d %5s", &dev_id, opt_buf);