On Mon, Nov 05, 2018 at 10:35:47AM +0000, Stefan Hajnoczi wrote:
> If the network stack calls .send_pkt()/.cancel_pkt() during .release(),
> a struct vhost_vsock use-after-free is possible. This occurs because
> .release() does not wait for other CPUs to stop using struct
> vhost_vsock.
>
> Switch to an RCU-enabled hashtable (indexed by guest CID) so that
> .release() can wait for other CPUs by calling synchronize_rcu(). This
> also eliminates vhost_vsock_lock acquisition in the data path so it
> could have a positive effect on performance.
>
> Reported-and-tested-by: syzbot+bd391451452fb0b93039@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+e3e074963495f92a89ed@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+d5a0a170c5069658b141@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
> ---
Michael,
This addresses CVE-2018-14625 kernel: use-after-free Read in
vhost_transport_send_pkt.
Please consider for -stable.
Stefan
> I have now manually tested the RCU hashtable fix and am happy with this
> patch.
>
> drivers/vhost/vsock.c | 57 +++++++++++++++++++++++++------------------
> 1 file changed, 33 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 34bc3ab40c6d..51879ed18652 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -15,6 +15,7 @@
> #include <net/sock.h>
> #include <linux/virtio_vsock.h>
> #include <linux/vhost.h>
> +#include <linux/hashtable.h>
>
> #include <net/af_vsock.h>
> #include "vhost.h"
> @@ -27,14 +28,14 @@ enum {
>
> /* Used to track all the vhost_vsock instances on the system. */
> static DEFINE_SPINLOCK(vhost_vsock_lock);
> -static LIST_HEAD(vhost_vsock_list);
> +static DEFINE_READ_MOSTLY_HASHTABLE(vhost_vsock_hash, 8);
>
> struct vhost_vsock {
> struct vhost_dev dev;
> struct vhost_virtqueue vqs[2];
>
> - /* Link to global vhost_vsock_list, protected by vhost_vsock_lock */
> - struct list_head list;
> + /* Link to global vhost_vsock_hash, writes use vhost_vsock_lock */
> + struct hlist_node hash;
>
> struct vhost_work send_pkt_work;
> spinlock_t send_pkt_list_lock;
> @@ -50,11 +51,14 @@ static u32 vhost_transport_get_local_cid(void)
> return VHOST_VSOCK_DEFAULT_HOST_CID;
> }
>
> -static struct vhost_vsock *__vhost_vsock_get(u32 guest_cid)
> +/* Callers that dereference the return value must hold vhost_vsock_lock or the
> + * RCU read lock.
> + */
> +static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
> {
> struct vhost_vsock *vsock;
>
> - list_for_each_entry(vsock, &vhost_vsock_list, list) {
> + hash_for_each_possible_rcu(vhost_vsock_hash, vsock, hash, guest_cid) {
> u32 other_cid = vsock->guest_cid;
>
> /* Skip instances that have no CID yet */
> @@ -69,17 +73,6 @@ static struct vhost_vsock *__vhost_vsock_get(u32 guest_cid)
> return NULL;
> }
>
> -static struct vhost_vsock *vhost_vsock_get(u32 guest_cid)
> -{
> - struct vhost_vsock *vsock;
> -
> - spin_lock_bh(&vhost_vsock_lock);
> - vsock = __vhost_vsock_get(guest_cid);
> - spin_unlock_bh(&vhost_vsock_lock);
> -
> - return vsock;
> -}
> -
> static void
> vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> struct vhost_virtqueue *vq)
> @@ -210,9 +203,12 @@ vhost_transport_send_pkt(struct virtio_vsock_pkt *pkt)
> struct vhost_vsock *vsock;
> int len = pkt->len;
>
> + rcu_read_lock();
> +
> /* Find the vhost_vsock according to guest context id */
> vsock = vhost_vsock_get(le64_to_cpu(pkt->hdr.dst_cid));
> if (!vsock) {
> + rcu_read_unlock();
> virtio_transport_free_pkt(pkt);
> return -ENODEV;
> }
> @@ -225,6 +221,8 @@ vhost_transport_send_pkt(struct virtio_vsock_pkt *pkt)
> spin_unlock_bh(&vsock->send_pkt_list_lock);
>
> vhost_work_queue(&vsock->dev, &vsock->send_pkt_work);
> +
> + rcu_read_unlock();
> return len;
> }
>
> @@ -234,12 +232,15 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> struct vhost_vsock *vsock;
> struct virtio_vsock_pkt *pkt, *n;
> int cnt = 0;
> + int ret = -ENODEV;
> LIST_HEAD(freeme);
>
> + rcu_read_lock();
> +
> /* Find the vhost_vsock according to guest context id */
> vsock = vhost_vsock_get(vsk->remote_addr.svm_cid);
> if (!vsock)
> - return -ENODEV;
> + goto out;
>
> spin_lock_bh(&vsock->send_pkt_list_lock);
> list_for_each_entry_safe(pkt, n, &vsock->send_pkt_list, list) {
> @@ -265,7 +266,10 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> vhost_poll_queue(&tx_vq->poll);
> }
>
> - return 0;
> + ret = 0;
> +out:
> + rcu_read_unlock();
> + return ret;
> }
>
> static struct virtio_vsock_pkt *
> @@ -533,10 +537,6 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
> spin_lock_init(&vsock->send_pkt_list_lock);
> INIT_LIST_HEAD(&vsock->send_pkt_list);
> vhost_work_init(&vsock->send_pkt_work, vhost_transport_send_pkt_work);
> -
> - spin_lock_bh(&vhost_vsock_lock);
> - list_add_tail(&vsock->list, &vhost_vsock_list);
> - spin_unlock_bh(&vhost_vsock_lock);
> return 0;
>
> out:
> @@ -577,9 +577,13 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
> struct vhost_vsock *vsock = file->private_data;
>
> spin_lock_bh(&vhost_vsock_lock);
> - list_del(&vsock->list);
> + if (vsock->guest_cid)
> + hash_del_rcu(&vsock->hash);
> spin_unlock_bh(&vhost_vsock_lock);
>
> + /* Wait for other CPUs to finish using vsock */
> + synchronize_rcu();
> +
> /* Iterating over all connections for all CIDs to find orphans is
> * inefficient. Room for improvement here. */
> vsock_for_each_connected_socket(vhost_vsock_reset_orphans);
> @@ -620,12 +624,17 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
>
> /* Refuse if CID is already in use */
> spin_lock_bh(&vhost_vsock_lock);
> - other = __vhost_vsock_get(guest_cid);
> + other = vhost_vsock_get(guest_cid);
> if (other && other != vsock) {
> spin_unlock_bh(&vhost_vsock_lock);
> return -EADDRINUSE;
> }
> +
> + if (vsock->guest_cid)
> + hash_del_rcu(&vsock->hash);
> +
> vsock->guest_cid = guest_cid;
> + hash_add_rcu(vhost_vsock_hash, &vsock->hash, guest_cid);
> spin_unlock_bh(&vhost_vsock_lock);
>
> return 0;
> --
> 2.19.1
>
Attachment:
signature.asc
Description: PGP signature
