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Date: Tue, 11 Dec 2012 14:30:12 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: pmoore@...hat.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, mprivozn@...hat.com
Subject: Re: [PATCH net-next rfc 2/2] tuntap: allow unpriveledge user to
enable and disable queues
On Tue, Dec 11, 2012 at 07:03:47PM +0800, Jason Wang wrote:
> Currently, when a file is attached to tuntap through TUNSETQUEUE, the uid/gid
> and CAP_NET_ADMIN were checked, and we use this ioctl to create and destroy
> queues. Sometimes, userspace such as qemu need to the ability to enable and
> disable a specific queue without priveledge since guest operating system may
> change the number of queues it want use.
>
> To support this kind of ability, this patch introduce a flag enabled which is
> used to track whether the queue is enabled by userspace. And also restrict that
> only one deivce could be used for a queue to attach. With this patch, the DAC
> checking when adding queues through IFF_ATTACH_QUEUE is still done and after
> this, IFF_DETACH_QUEUE/IFF_ATTACH_QUEUE could be used to disable/enable this
> queue.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> drivers/net/tun.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 files changed, 73 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index d593f56..43831a7 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -138,6 +138,7 @@ struct tun_file {
> /* only used for fasnyc */
> unsigned int flags;
> u16 queue_index;
> + bool enabled;
> };
>
> struct tun_flow_entry {
> @@ -345,9 +346,11 @@ unlock:
> static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
> {
> struct tun_struct *tun = netdev_priv(dev);
> + struct tun_file *tfile;
> struct tun_flow_entry *e;
> u32 txq = 0;
> u32 numqueues = 0;
> + int i;
>
> rcu_read_lock();
> numqueues = tun->numqueues;
> @@ -366,6 +369,19 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb)
> txq -= numqueues;
> }
>
> + tfile = rcu_dereference(tun->tfiles[txq]);
> + if (unlikely(!tfile->enabled))
This unlikely tag is suspicious. It should be perfectly
legal to use less queues than created.
> + /* tun_detach() should make sure there's at least one queue
> + * could be used to do the tranmission.
> + */
> + for (i = 0; i < numqueues; i++) {
> + tfile = rcu_dereference(tun->tfiles[i]);
> + if (tfile->enabled) {
> + txq = i;
> + break;
> + }
> + }
> +
Worst case this will do a linear scan over all queueus on each packet.
Instead, I think we need a list of all queues and only install
the active ones in the array.
> rcu_read_unlock();
> return txq;
> }
> @@ -386,6 +402,36 @@ static void tun_set_real_num_queues(struct tun_struct *tun)
> netif_set_real_num_rx_queues(tun->dev, tun->numqueues);
> }
>
> +static int tun_enable(struct tun_file *tfile)
> +{
> + if (tfile->enabled == true)
simply if (tfile->enabled)
> + return -EINVAL;
Actually it's better to have operations be
idempotent. If it's enabled, enabling should
be a NOP not an error.
> +
> + tfile->enabled = true;
> + return 0;
> +}
> +
> +static int tun_disable(struct tun_file *tfile)
> +{
> + struct tun_struct *tun = rcu_dereference_protected(tfile->tun,
> + lockdep_rtnl_is_held());
> + u16 index = tfile->queue_index;
> +
> + if (!tun)
> + return -EINVAL;
> +
> + if (tun->numqueues == 1)
> + return -EINVAL;
So if there's a single queue we can't disable it,
but if there are > 1 we can disable them all.
This seems arbitrary.
> +
> + BUG_ON(index >= tun->numqueues);
> + tfile->enabled = false;
> +
> + synchronize_net();
> + tun_flow_delete_by_queue(tun, index);
> +
> + return 0;
> +}
> +
> static void __tun_detach(struct tun_file *tfile, bool clean)
> {
> struct tun_file *ntfile;
> @@ -446,6 +492,7 @@ static void tun_detach_all(struct net_device *dev)
> BUG_ON(!tfile);
> wake_up_all(&tfile->wq.wait);
> rcu_assign_pointer(tfile->tun, NULL);
> + tfile->enabled = false;
> --tun->numqueues;
> }
> BUG_ON(tun->numqueues != 0);
> @@ -490,6 +537,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
> rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
> sock_hold(&tfile->sk);
> tun->numqueues++;
> + tfile->enabled = true;
>
> tun_set_real_num_queues(tun);
>
> @@ -672,6 +720,10 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
> if (txq >= tun->numqueues)
> goto drop;
>
> + /* Drop packet if the queue was not enabled */
> + if (!tfile->enabled)
> + goto drop;
> +
> tun_debug(KERN_INFO, tun, "tun_net_xmit %d\n", skb->len);
>
> BUG_ON(!tfile);
> @@ -1010,6 +1062,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
> bool zerocopy = false;
> int err;
>
> + if (!tfile->enabled)
> + return -EINVAL;
> +
> if (!(tun->flags & TUN_NO_PI)) {
> if ((len -= sizeof(pi)) > total_len)
> return -EINVAL;
> @@ -1199,6 +1254,9 @@ static ssize_t tun_put_user(struct tun_struct *tun,
> struct tun_pi pi = { 0, skb->protocol };
> ssize_t total = 0;
>
> + if (!tfile->enabled)
> + return -EINVAL;
> +
> if (!(tun->flags & TUN_NO_PI)) {
> if ((len -= sizeof(pi)) < 0)
> return -EINVAL;
> @@ -1769,15 +1827,21 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
> if (dev->netdev_ops != &tap_netdev_ops &&
> dev->netdev_ops != &tun_netdev_ops)
> ret = -EINVAL;
> - else if (tun_not_capable(tun))
> - ret = -EPERM;
> - /* TUNSETIFF is needed to do permission checking */
> - else if (tun->numqueues == 0)
> - ret = -EPERM;
> - else
> - ret = tun_attach(tun, file);
> + else {
> + if (!rcu_dereference(tfile->tun)) {
Should be rcu_dereference_protected.
> + if (tun_not_capable(tun) ||
> + tun->numqueues == 0)
> + ret = -EPERM;
> + else
> + ret = tun_attach(tun, file);
> + }
> + else {
> + /* FIXME: permission check? */
> + ret = tun_enable(tfile);
> + }
> + }
> } else if (ifr->ifr_flags & IFF_DETACH_QUEUE)
> - __tun_detach(tfile, false);
> + tun_disable(tfile);
> else
> ret = -EINVAL;
>
> @@ -2085,6 +2149,7 @@ static int tun_chr_open(struct inode *inode, struct file * file)
> tfile->socket.file = file;
> tfile->socket.ops = &tun_socket_ops;
>
> + tfile->enabled = false;
> sock_init_data(&tfile->socket, &tfile->sk);
> sk_change_net(&tfile->sk, tfile->net);
>
> --
> 1.7.1
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