[PATCH 5.4 109/132] rbd: require global CAP_SYS_ADMIN for mapping and unmapping

Greg Kroah-Hartman
2020-09-15T23:57:41Z

From: Ilya Dryomov <idryomov@gmail.com>

commit f44d04e696feaf13d192d942c4f14ad2e117065a upstream.

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

---
drivers/block/rbd.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -5280,6 +5280,9 @@ static ssize_t rbd_config_info_show(stru
{
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);
}

@@ -5391,6 +5394,9 @@ static ssize_t rbd_image_refresh(struct
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_typ
struct rbd_client *rbdc;
int rc;

+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
if (!try_module_get(THIS_MODULE))
return -ENODEV;

@@ -7208,6 +7217,9 @@ static ssize_t do_rbd_remove(struct 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);