netdev - Re: [PATCH] net: fix shift-out-of-bounds in nl802154_new

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Date:   Tue, 6 Apr 2021 08:21:04 -0400
From:   Alexander Aring <alex.aring@...il.com>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     Stefan Schmidt <stefan@...enfreihafen.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wpan - ML <linux-wpan@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        syzbot <syzbot+7bf7b22759195c9a21e9@...kaller.appspotmail.com>
Subject: Re: [PATCH] net: fix shift-out-of-bounds in nl802154_new_interface

Hi,

On Mon, 5 Apr 2021 at 15:58, Pavel Skripkin <paskripkin@...il.com> wrote:
>
> syzbot reported shift-out-of-bounds in nl802154_new_interface.
> The problem was in signed representation of enum nl802154_iftype
>
> enum nl802154_iftype {
>         /* for backwards compatibility TODO */
>         NL802154_IFTYPE_UNSPEC = -1,
> ...
>
> Since, enum has negative value in it, objects of this type
> will be represented as signed integer.
>
>         type = nla_get_u32(info->attrs[NL802154_ATTR_IFTYPE]);
>
> u32 will be casted to signed, which can cause negative value type.
>
> Reported-by: syzbot+7bf7b22759195c9a21e9@...kaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>

Yes, this patch will fix the issue but we discussed that the problem
is deeper than such a fix. The real problem is that we are using a -1
value which doesn't fit into the u32 netlink value and it gets
converted back and forward which we should avoid.

- Alex