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Subject[PATCH 4.4 19/46] rbd: require global CAP_SYS_ADMIN for mapping and unmapping
Date
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 | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3945,6 +3945,9 @@ 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;
@@ -5404,6 +5407,9 @@ static ssize_t do_rbd_add(struct bus_typ
bool read_only;
int rc;

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

@@ -5548,6 +5554,9 @@ static ssize_t do_rbd_remove(struct bus_
bool already = false;
int ret;

+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
ret = kstrtoul(buf, 10, &ul);
if (ret)
return ret;

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