This is a note to let you know that I've just added the patch titled
Fix double fget() in vhost_net_set_backend()
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fix-double-fget-in-vhost_net_set_backend.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From fb4554c2232e44d595920f4d5c66cf8f7d13f9bc Mon Sep 17 00:00:00 2001
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Mon, 16 May 2022 16:42:13 +0800
Subject: Fix double fget() in vhost_net_set_backend()
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxx
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
[4.14: Account for get_tap_skb_array() instead of get_tap_ptr_ring()]
Signed-off-by: Samuel Mendoza-Jonas <samjonas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/vhost/net.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -1047,13 +1047,9 @@ err:
return ERR_PTR(r);
}
-static struct skb_array *get_tap_skb_array(int fd)
+static struct skb_array *get_tap_skb_array(struct file *file)
{
struct skb_array *array;
- struct file *file = fget(fd);
-
- if (!file)
- return NULL;
array = tun_get_skb_array(file);
if (!IS_ERR(array))
goto out;
@@ -1062,7 +1058,6 @@ static struct skb_array *get_tap_skb_arr
goto out;
array = NULL;
out:
- fput(file);
return array;
}
@@ -1143,8 +1138,12 @@ static long vhost_net_set_backend(struct
vhost_net_disable_vq(n, vq);
vq->private_data = sock;
vhost_net_buf_unproduce(nvq);
- if (index == VHOST_NET_VQ_RX)
- nvq->rx_array = get_tap_skb_array(fd);
+ if (index == VHOST_NET_VQ_RX) {
+ if (sock)
+ nvq->rx_array = get_tap_skb_array(sock->file);
+ else
+ nvq->rx_array = NULL;
+ }
r = vhost_vq_init_access(vq);
if (r)
goto err_used;
Patches currently in stable-queue which might be from viro@xxxxxxxxxxxxxxxxxx are
queue-4.14/fix-double-fget-in-vhost_net_set_backend.patch
