netdev - Re: [PATCH] openvswitch: Avoid OOB read when parsing flow nlattrs

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Message-ID: <CAOrHB_BR6JhBOiYL6=-_t=G+g58TKB3s8NBF65s3txTYn+35pw@mail.gmail.com>
Date:   Mon, 14 Jan 2019 16:19:34 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Ross Lagerwall <ross.lagerwall@...rix.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        ovs dev <dev@...nvswitch.org>
Subject: Re: [PATCH] openvswitch: Avoid OOB read when parsing flow nlattrs

On Mon, Jan 14, 2019 at 1:17 AM Ross Lagerwall
<ross.lagerwall@...rix.com> wrote:
>
> For nested and variable attributes, the expected length of an attribute
> is not known and marked by a negative number.  This results in an OOB
> read when the expected length is later used to check if the attribute is
> all zeros. Fix this by using the actual length of the attribute rather
> than the expected length.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
> ---
>  net/openvswitch/flow_netlink.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> index 435a4bdf8f89..691da853bef5 100644
> --- a/net/openvswitch/flow_netlink.c
> +++ b/net/openvswitch/flow_netlink.c
> @@ -500,7 +500,7 @@ static int __parse_flow_nlattrs(const struct nlattr *attr,
>                         return -EINVAL;
>                 }
>
> -               if (!nz || !is_all_zero(nla_data(nla), expected_len)) {
> +               if (!nz || !is_all_zero(nla_data(nla), nla_len(nla))) {
>                         attrs |= 1 << type;
>                         a[type] = nla;
>                 }

Good Catch.
Acked-by: Pravin B Shelar <pshelar@....org>