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Date: Mon, 17 May 2021 20:12:41 +0530
From: Prasanna Kalever <pkalever@...hat.com>
To: josef@...icpanda.com, axboe@...nel.dk,
Ming Lei <ming.lei@...hat.com>
Cc: Prasanna Kumar Kalever <prasanna.kalever@...hat.com>,
linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
nbd@...er.debian.org, Ilya Dryomov <idryomov@...hat.com>,
Xiubo Li <xiubli@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH] nbd: provide a way for userspace processes to identify
device backends
On Fri, Apr 30, 2021 at 7:44 AM Xiubo Li <xiubli@...hat.com> wrote:
>
> On 2021/4/29 18:28, Prasanna Kumar Kalever wrote:
> > Problem:
> > On reconfigure of device, there is no way to defend if the backend
> > storage is matching with the initial backend storage.
> >
> > Say, if an initial connect request for backend "pool1/image1" got
> > mapped to /dev/nbd0 and the userspace process is terminated. A next
> > reconfigure request within NBD_ATTR_DEAD_CONN_TIMEOUT is allowed to
> > use /dev/nbd0 for a different backend "pool1/image2"
> >
> > For example, an operation like below could be dangerous:
> >
> > $ sudo rbd-nbd map --try-netlink rbd-pool/ext4-image
> > /dev/nbd0
> > $ sudo blkid /dev/nbd0
> > /dev/nbd0: UUID="bfc444b4-64b1-418f-8b36-6e0d170cfc04" TYPE="ext4"
> > $ sudo pkill -9 rbd-nbd
> > $ sudo rbd-nbd attach --try-netlink --device /dev/nbd0 rbd-pool/xfs-image
> > /dev/nbd0
> > $ sudo blkid /dev/nbd0
> > /dev/nbd0: UUID="d29bf343-6570-4069-a9ea-2fa156ced908" TYPE="xfs"
> >
> > Solution:
> > Provide a way for userspace processes to keep some metadata to identify
> > between the device and the backend, so that when a reconfigure request is
> > made, we can compare and avoid such dangerous operations.
> >
> > With this solution, as part of the initial connect request, backend
> > path can be stored in the sysfs per device config, so that on a reconfigure
> > request it's easy to check if the backend path matches with the initial
> > connect backend path.
> >
> > Please note, ioctl interface to nbd will not have these changes, as there
> > won't be any reconfigure.
> >
> > Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@...hat.com>
> > ---
> > drivers/block/nbd.c | 60 +++++++++++++++++++++++++++++++-
> > include/uapi/linux/nbd-netlink.h | 1 +
> > 2 files changed, 60 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > index 4ff71b579cfc..b5022187ad9c 100644
> > --- a/drivers/block/nbd.c
> > +++ b/drivers/block/nbd.c
> > @@ -79,6 +79,7 @@ struct link_dead_args {
> > #define NBD_RT_HAS_CONFIG_REF 4
> > #define NBD_RT_BOUND 5
> > #define NBD_RT_DISCONNECT_ON_CLOSE 6
> > +#define NBD_RT_HAS_BACKEND_FILE 7
> >
> > #define NBD_DESTROY_ON_DISCONNECT 0
> > #define NBD_DISCONNECT_REQUESTED 1
> > @@ -119,6 +120,8 @@ struct nbd_device {
> >
> > struct completion *destroy_complete;
> > unsigned long flags;
> > +
> > + char *backend;
> > };
> >
> > #define NBD_CMD_REQUEUED 1
> > @@ -216,6 +219,20 @@ static const struct device_attribute pid_attr = {
> > .show = pid_show,
> > };
> >
> > +static ssize_t backend_show(struct device *dev,
> > + struct device_attribute *attr, char *buf)
> > +{
> > + struct gendisk *disk = dev_to_disk(dev);
> > + struct nbd_device *nbd = (struct nbd_device *)disk->private_data;
> > +
> > + return sprintf(buf, "%s\n", nbd->backend ?: "");
> > +}
> > +
> > +static const struct device_attribute backend_attr = {
> > + .attr = { .name = "backend", .mode = 0444},
> > + .show = backend_show,
> > +};
> > +
> > static void nbd_dev_remove(struct nbd_device *nbd)
> > {
> > struct gendisk *disk = nbd->disk;
> > @@ -1215,6 +1232,12 @@ static void nbd_config_put(struct nbd_device *nbd)
> > &config->runtime_flags))
> > device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
> > nbd->task_recv = NULL;
> > + if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
> > + &config->runtime_flags)) {
> > + device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
> > + kfree(nbd->backend);
> > + nbd->backend = NULL;
> > + }
> > nbd_clear_sock(nbd);
> > if (config->num_connections) {
> > int i;
> > @@ -1274,7 +1297,7 @@ static int nbd_start_device(struct nbd_device *nbd)
> >
> > error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
> > if (error) {
> > - dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n");
> > + dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
> > return error;
> > }
> > set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
> > @@ -1681,6 +1704,7 @@ static int nbd_dev_add(int index)
> > BLK_MQ_F_BLOCKING;
> > nbd->tag_set.driver_data = nbd;
> > nbd->destroy_complete = NULL;
> > + nbd->backend = NULL;
> >
> > err = blk_mq_alloc_tag_set(&nbd->tag_set);
> > if (err)
> > @@ -1754,6 +1778,7 @@ static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
> > [NBD_ATTR_SOCKETS] = { .type = NLA_NESTED},
> > [NBD_ATTR_DEAD_CONN_TIMEOUT] = { .type = NLA_U64 },
> > [NBD_ATTR_DEVICE_LIST] = { .type = NLA_NESTED},
> > + [NBD_ATTR_BACKEND_IDENTIFIER] = { .type = NLA_STRING},
> > };
> >
> > static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
> > @@ -1956,6 +1981,23 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
> > }
> > }
> > ret = nbd_start_device(nbd);
> > + if (ret)
> > + goto out;
> > + if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
> > + nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
> > + GFP_KERNEL);
> > + if (!nbd->backend) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > + }
> > + ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
> > + if (ret) {
> > + dev_err(disk_to_dev(nbd->disk),
> > + "device_create_file failed for backend!\n");
> > + goto out;
> > + }
> > + set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
> > out:
> > mutex_unlock(&nbd->config_lock);
> > if (!ret) {
> > @@ -2048,6 +2090,22 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
> > index);
> > return -EINVAL;
> > }
> > + if (nbd->backend) {
> > + if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
> > + if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
> > + nbd->backend)) {
> > + mutex_unlock(&nbd_index_mutex);
> > + dev_err(nbd_to_dev(nbd),
> > + "backend image doesn't match with %s\n",
> > + nbd->backend);
> > + return -EINVAL;
> > + }
> > + } else {
> > + mutex_unlock(&nbd_index_mutex);
> > + dev_err(nbd_to_dev(nbd), "must specify backend\n");
> > + return -EINVAL;
> > + }
> > + }
> > if (!refcount_inc_not_zero(&nbd->refs)) {
> > mutex_unlock(&nbd_index_mutex);
> > printk(KERN_ERR "nbd: device at index %d is going down\n",
> > diff --git a/include/uapi/linux/nbd-netlink.h b/include/uapi/linux/nbd-netlink.h
> > index c5d0ef7aa7d5..2d0b90964227 100644
> > --- a/include/uapi/linux/nbd-netlink.h
> > +++ b/include/uapi/linux/nbd-netlink.h
> > @@ -35,6 +35,7 @@ enum {
> > NBD_ATTR_SOCKETS,
> > NBD_ATTR_DEAD_CONN_TIMEOUT,
> > NBD_ATTR_DEVICE_LIST,
> > + NBD_ATTR_BACKEND_IDENTIFIER,
> > __NBD_ATTR_MAX,
> > };
> > #define NBD_ATTR_MAX (__NBD_ATTR_MAX - 1)
>
> Reviewed-by: Xiubo Li <xiubli@...hat.com>
Thank you Xiubo Li.
Assuming this patch got lost, attempting to bring this patch onto the
top with a friendly reminder.
I sincerely request the maintainers to please take a look.
Many Thanks!
--
Prasanna
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