netdev - Re: [PATCH bpf] xsk: fix incorrect netdev reference count

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Date:   Mon, 23 Nov 2020 09:28:29 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Marek Majtyka <alardam@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Marek Majtyka <marekx.majtyka@...el.com>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf] xsk: fix incorrect netdev reference count

On Fri, Nov 20, 2020 at 4:17 PM <alardam@...il.com> wrote:
>
> From: Marek Majtyka <marekx.majtyka@...el.com>
>
> Fix incorrect netdev reference count in xsk_bind operation. Incorrect
> reference count of the device appears when a user calls bind with the
> XDP_ZEROCOPY flag on an interface which does not support zero-copy.
> In such a case, an error is returned but the reference count is not
> decreased. This change fixes the fault, by decreasing the reference count
> in case of such an error.
>
> The problem being corrected appeared in '162c820ed896' for the first time,
> and the code was moved to new file location over the time with commit
> 'c2d3d6a47462'. This specific patch applies to all version starting
> from 'c2d3d6a47462'. The same solution should be applied but on different
> file (net/xdp/xdp_umem.c) and function (xdp_umem_assign_dev) for versions
> from '162c820ed896' to 'c2d3d6a47462' excluded.
>
> Fixes: 162c820ed896 ("xdp: hold device for umem regardless of zero- ...")
> Signed-off-by: Marek Majtyka <marekx.majtyka@...el.com>
> ---
>  net/xdp/xsk_buff_pool.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index 8a3bf4e1318e..46d09bfb1923 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -185,8 +185,10 @@ static int __xp_assign_dev(struct xsk_buff_pool *pool,
>  err_unreg_pool:
>         if (!force_zc)
>                 err = 0; /* fallback to copy mode */
> -       if (err)
> +       if (err) {
>                 xsk_clear_pool_at_qid(netdev, queue_id);
> +               dev_put(netdev);
> +       }
>         return err;
>  }

Thank you Marek for spotting and fixing this!

Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

> --
> 2.27.0
>