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Fix double fget() in vhost_net_set_backend()

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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>
This commit is contained in:
Al Viro 2022-05-16 16:42:13 +08:00
parent a91714312e
commit fb4554c223
1 changed files with 7 additions and 8 deletions
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15
drivers/vhost/net.c
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@ -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(int fd)
goto out;
ring = NULL;
out:
fput(file);
return ring;
}
@ -1552,8 +1547,12 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
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;