On Wed, Aug 30, 2023 at 05:17:03PM +0200, Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
>
> Fix a use-after-free error that is possible if the xsk_diag interface
> is used at the same time as the socket is being closed. In the early
I thought our understanding is: socket is alive, we use diag interface
against it but netdev that we bound socket to is being torn down.
since xs->dev was freed but not NULLed, xsk_diag_put_info() uses this ptr
to retrieve ifindex.
> days of AF_XDP, the way we tested that a socket was not bound or being
> closed was to simply check if the netdevice pointer in the xsk socket
> structure was NULL. Later, a better system was introduced by having an
> explicit state variable in the xsk socket struct. For example, the
> state of a socket that is going down is XSK_UNBOUND.
>
> The commit in the Fixes tag below deleted the old way of signalling
> that a socket is going down, setting dev to NULL. This in the belief
> that all code using the old way had been exterminated. That was
> unfortunately not true as the xsk diagnostics code was still using the
> old way and thus does not work as intended when a socket is going
> down. Fix this by introducing a test against the state variable. If
Again, I believe it was not the socket going down but rather the netdev?
> the socket is going down, simply abort the diagnostic's netlink
> operation.
>
> Fixes: 18b1ab7aa76b ("xsk: Fix race at socket teardown")
> Reported-by: syzbot+822d1359297e2694f873@xxxxxxxxxxxxxxxxxxxxxxxxx
Nit: I see syzbot wanted you to include:
Reported-and-tested-by: syzbot+822d13...@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> ---
> net/xdp/xsk_diag.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/net/xdp/xsk_diag.c b/net/xdp/xsk_diag.c
> index c014217f5fa7..da3100bfa1c5 100644
> --- a/net/xdp/xsk_diag.c
> +++ b/net/xdp/xsk_diag.c
> @@ -111,6 +111,9 @@ static int xsk_diag_fill(struct sock *sk, struct sk_buff *nlskb,
> sock_diag_save_cookie(sk, msg->xdiag_cookie);
>
> mutex_lock(&xs->mutex);
> + if (xs->state == XSK_UNBOUND)
> + goto out_nlmsg_trim;
With the above I feel like we can get rid of xs->dev test in
xsk_diag_put_info(), no?
> +
> if ((req->xdiag_show & XDP_SHOW_INFO) && xsk_diag_put_info(xs, nlskb))
> goto out_nlmsg_trim;
>
>
> base-commit: 35d2b7ffffc1d9b3dc6c761010aa3338da49165b
> --
> 2.42.0
>
