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SubjectRe: [PATCH] nbd: provide a way for userspace processes to identify device backends
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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@redhat.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@redhat.com>

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