From: Al Viro viro@zeniv.linux.org.uk
commit fb4554c2232e44d595920f4d5c66cf8f7d13f9bc upstream.
Descriptor table is a shared resource; two fget() on the same descriptor may return different struct file references. get_tap_ptr_ring() is called after we'd found (and pinned) the socket we'll be using and it tries to find the private tun/tap data structures associated with it. Redoing the lookup by the same file descriptor we'd used to get the socket is racy - we need to same struct file.
Thanks to Jason for spotting a braino in the original variant of patch - I'd missed the use of fd == -1 for disabling backend, and in that case we can end up with sock == NULL and sock != oldsock.
Cc: stable@kernel.org Acked-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Jason Wang jasowang@redhat.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/vhost/net.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
--- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -1450,13 +1450,9 @@ err: return ERR_PTR(r); }
-static struct ptr_ring *get_tap_ptr_ring(int fd) +static struct ptr_ring *get_tap_ptr_ring(struct file *file) { struct ptr_ring *ring; - struct file *file = fget(fd); - - if (!file) - return NULL; ring = tun_get_tx_ring(file); if (!IS_ERR(ring)) goto out; @@ -1465,7 +1461,6 @@ static struct ptr_ring *get_tap_ptr_ring goto out; ring = NULL; out: - fput(file); return ring; }
@@ -1552,8 +1547,12 @@ static long vhost_net_set_backend(struct r = vhost_net_enable_vq(n, vq); if (r) goto err_used; - if (index == VHOST_NET_VQ_RX) - nvq->rx_ring = get_tap_ptr_ring(fd); + if (index == VHOST_NET_VQ_RX) { + if (sock) + nvq->rx_ring = get_tap_ptr_ring(sock->file); + else + nvq->rx_ring = NULL; + }
oldubufs = nvq->ubufs; nvq->ubufs = ubufs;