linux-kernel - Re: [PATCH v3] wifi: mwifiex: Fix oob check condition in mwifiex_process_rx

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Date:   Thu, 14 Sep 2023 15:09:47 +0800
From:   Pin-yen Lin <treapking@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     linux-wireless@...r.kernel.org, Kalle Valo <kvalo@...nel.org>,
        Polaris Pi <pinkperfect2021@...il.com>,
        Matthew Wang <matthewmwang@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] wifi: mwifiex: Fix oob check condition in mwifiex_process_rx_packet

Hi Brian,

Thanks for the review.

On Thu, Sep 14, 2023 at 4:31 AM Brian Norris <briannorris@...omium.org> wrote:
>
> On Fri, Sep 08, 2023 at 06:41:12PM +0800, Pin-yen Lin wrote:
> > Only skip the code path trying to access the rfc1042 headers when the
> > buffer is too small, so the driver can still process packets without
> > rfc1042 headers.
> >
> > Fixes: 119585281617 ("wifi: mwifiex: Fix OOB and integer underflow when rx packets")
> > Signed-off-by: Pin-yen Lin <treapking@...omium.org>
>
> I'd appreciate another review/test from one of the others here
> (Matthew?), even though I know y'all are already working together.
>
> > ---
> >
> > Changes in v3:
> > - Really apply the sizeof call fix as it was missed in the previous patch
> >
> > Changes in v2:
> > - Fix sizeof call (sizeof(rx_pkt_hdr) --> sizeof(*rx_pkt_hdr))
> >
> >  drivers/net/wireless/marvell/mwifiex/sta_rx.c | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/net/wireless/marvell/mwifiex/sta_rx.c b/drivers/net/wireless/marvell/mwifiex/sta_rx.c
> > index 65420ad67416..257737137cd7 100644
> > --- a/drivers/net/wireless/marvell/mwifiex/sta_rx.c
> > +++ b/drivers/net/wireless/marvell/mwifiex/sta_rx.c
> > @@ -86,7 +86,8 @@ int mwifiex_process_rx_packet(struct mwifiex_private *priv,
> >       rx_pkt_len = le16_to_cpu(local_rx_pd->rx_pkt_length);
> >       rx_pkt_hdr = (void *)local_rx_pd + rx_pkt_off;
> >
> > -     if (sizeof(*rx_pkt_hdr) + rx_pkt_off > skb->len) {
> > +     if (sizeof(rx_pkt_hdr->eth803_hdr) + sizeof(rfc1042_header) +
> > +         rx_pkt_off > skb->len) {
> >               mwifiex_dbg(priv->adapter, ERROR,
> >                           "wrong rx packet offset: len=%d, rx_pkt_off=%d\n",
> >                           skb->len, rx_pkt_off);
> > @@ -95,12 +96,13 @@ int mwifiex_process_rx_packet(struct mwifiex_private *priv,
> >               return -1;
> >       }
> >
> > -     if ((!memcmp(&rx_pkt_hdr->rfc1042_hdr, bridge_tunnel_header,
> > -                  sizeof(bridge_tunnel_header))) ||
> > -         (!memcmp(&rx_pkt_hdr->rfc1042_hdr, rfc1042_header,
> > -                  sizeof(rfc1042_header)) &&
> > -          ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_AARP &&
> > -          ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_IPX)) {
> > +     if (sizeof(*rx_pkt_hdr) + rx_pkt_off <= skb->len &&
>
> Are you sure you want this length check to fall back to the non-802.3
> codepath? Isn't it an error to look like an 802.3 frame but to be too
> small? I'd think we want to drop such packets, not process them as-is.

I did that because I saw other drivers (e.g., [1], [2]) use similar
approaches, and I assumed that the rest of the pipeline will
eventually drop it if the packet cannot be recognized. But, yes, we
can just drop the packet here if it doesn't look good.

[1]: https://elixir.bootlin.com/linux/latest/source/drivers/net/wireless/intersil/hostap/hostap_80211_rx.c#L1035
[2]: https://elixir.bootlin.com/linux/latest/source/drivers/net/wireless/intel/ipw2x00/libipw_rx.c#L735
>
> If I'm correct, then this check should move inside the 'if' branch of
> this if/else.

We can't simply move the check inside the if branch because the
condition also checks rx_pkt_hdr->rfc1042_hdr.snap_type. Though, of
course, it is doable by adding another `if` conditions.
>
> Brian
>

Regards,
Pin-yen

> > +         ((!memcmp(&rx_pkt_hdr->rfc1042_hdr, bridge_tunnel_header,
> > +                   sizeof(bridge_tunnel_header))) ||
> > +          (!memcmp(&rx_pkt_hdr->rfc1042_hdr, rfc1042_header,
> > +                   sizeof(rfc1042_header)) &&
> > +           ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_AARP &&
> > +           ntohs(rx_pkt_hdr->rfc1042_hdr.snap_type) != ETH_P_IPX))) {
> >               /*
> >                *  Replace the 803 header and rfc1042 header (llc/snap) with an
> >                *    EthernetII header, keep the src/dst and snap_type
> > --
> > 2.42.0.283.g2d96d420d3-goog
> >