4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stefan Hajnoczi stefanha@redhat.com
commit 834e772c8db0c6a275d75315d90aba4ebbb1e249 upstream.
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.
This is CVE-2018-14625 "kernel: use-after-free Read in vhost_transport_send_pkt".
Cc: stable@vger.kernel.org Reported-and-tested-by: syzbot+bd391451452fb0b93039@syzkaller.appspotmail.com Reported-by: syzbot+e3e074963495f92a89ed@syzkaller.appspotmail.com Reported-by: syzbot+d5a0a170c5069658b141@syzkaller.appspotmail.com Signed-off-by: Stefan Hajnoczi stefanha@redhat.com Signed-off-by: Michael S. Tsirkin mst@redhat.com Acked-by: Jason Wang jasowang@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/vhost/vsock.c | 57 ++++++++++++++++++++++++++++---------------------- 1 file changed, 33 insertions(+), 24 deletions(-)
--- 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 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 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_v 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_v 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_ 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_ 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 i 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(struc 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 vh
/* 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;