linux-kernel - Re: [PATCH v1] gve: fix the wrong AdminQ buffer overflow check

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Message-ID: <CAH_-1qzu_X26sUehY9721+yG3xYVw_0eiPGb=0X4p0m7Jv+ddg@mail.gmail.com>
Date:   Wed, 14 Jul 2021 15:45:09 -0700
From:   Catherine Sullivan <csully@...gle.com>
To:     Haiyue Wang <haiyue.wang@...el.com>
Cc:     netdev@...r.kernel.org, Sagi Shahar <sagis@...gle.com>,
        Jon Olson <jonolson@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        David Awogbemila <awogbemila@...gle.com>,
        Yangchun Fu <yangchun@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Bailey Forrest <bcf@...gle.com>, Kuo Zhao <kuozhao@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] gve: fix the wrong AdminQ buffer overflow check

On Wed, Jul 14, 2021 at 12:58 AM Haiyue Wang <haiyue.wang@...el.com> wrote:
>
> The 'tail' pointer is also free-running count, so it needs to be masked
> as 'adminq_prod_cnt' does, to become an index value of AdminQ buffer.
>
> Fixes: 5cdad90de62c ("gve: Batch AQ commands for creating and destroying queues.")
> Signed-off-by: Haiyue Wang <haiyue.wang@...el.com>

Reviewed-by: Catherine Sullivan <csully@...gle.com>

> ---
>  drivers/net/ethernet/google/gve/gve_adminq.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/google/gve/gve_adminq.c b/drivers/net/ethernet/google/gve/gve_adminq.c
> index 5bb56b454541..f089d33dd48e 100644
> --- a/drivers/net/ethernet/google/gve/gve_adminq.c
> +++ b/drivers/net/ethernet/google/gve/gve_adminq.c
> @@ -322,7 +322,8 @@ static int gve_adminq_issue_cmd(struct gve_priv *priv,
>         tail = ioread32be(&priv->reg_bar0->adminq_event_counter);
>
>         // Check if next command will overflow the buffer.
> -       if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) == tail) {
> +       if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) ==
> +           (tail & priv->adminq_mask)) {
>                 int err;
>
>                 // Flush existing commands to make room.
> @@ -332,7 +333,8 @@ static int gve_adminq_issue_cmd(struct gve_priv *priv,
>
>                 // Retry.
>                 tail = ioread32be(&priv->reg_bar0->adminq_event_counter);
> -               if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) == tail) {
> +               if (((priv->adminq_prod_cnt + 1) & priv->adminq_mask) ==
> +                   (tail & priv->adminq_mask)) {
>                         // This should never happen. We just flushed the
>                         // command queue so there should be enough space.
>                         return -ENOMEM;
> --
> 2.32.0
>

Thanks!