Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
        Jeff Layton <jlayton@kernel.org>
Subject: [PATCH 4.19 63/78] rbd: require global CAP_SYS_ADMIN for mapping and unmapping
Date:   Tue, 15 Sep 2020 16:13:28 +0200
Message-Id: <20200915140636.727772488@linuxfoundation.org>
In-Reply-To: <20200915140633.552502750@linuxfoundation.org>
References: <20200915140633.552502750@linuxfoundation.org>
User-Agent: quilt/0.66
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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
@@ -4124,6 +4124,9 @@ 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);
 }
 
@@ -4235,6 +4238,9 @@ 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;
@@ -5846,6 +5852,9 @@ 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;
 
@@ -5995,6 +6004,9 @@ 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);