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 <20210122001326.14263-2-sonnysasaka@chromium.org> <CABBYNZJs_rzBSHOjvqg5F4u6gxX7LcNUc77KtzHEr5L7Y5Zd-A@mail.gmail.com>
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From:   Sonny Sasaka <sonnysasaka@chromium.org>
Date:   Thu, 21 Jan 2021 17:24:56 -0800
Message-ID: <CAO271mkMtmDm_MayCX-+Dddg3aL1uv=GD3egCGJ6gDCEHowp8g@mail.gmail.com>
Subject: Re: [PATCH BlueZ v2 2/2] input/hog: Do not create UHID if report map
 is broken
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>
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Hi Luiz,

On Thu, Jan 21, 2021 at 4:37 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Sonny,
>
> On Thu, Jan 21, 2021 at 4:18 PM Sonny Sasaka <sonnysasaka@chromium.org> wrote:
> >
> > The report map in the cache could be dirty, for example when reading a
> > report map from peer was cancelled, we should be able to detect it and
> > not try to create UHID. Instead we will read it again from the peer.
>
> Don't we clean the cache if it had failed? Or you meant to say the
> read long procedure was not complete so we got just part of the report
> map?
Looks like this is the case. It happened to me once when I cancel
reconnection (trigger pairing mode during reconnection) from the
keyboard side. It's hard to confirm since I have to get the timing
right.

> In that case we should have failed
I agree. However it seems that the code already tries to fail by
looking at the status inside report_map_read_cb, but somehow it still
gets through. It could be the keyboard bug that we have to detect
anyway?

> also if we need to protect
> uhid from malformed report map, which sounds like a kernel bug, then
> we should at least have it inside bt_uhid instance so we can at least
> attempt to have some unit testing done with broken report maps.
>
> > ---
> >  profiles/input/hog-lib.c | 21 ++++++++++++++++++---
> >  1 file changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/profiles/input/hog-lib.c b/profiles/input/hog-lib.c
> > index 089f42826..d6a3bda4d 100644
> > --- a/profiles/input/hog-lib.c
> > +++ b/profiles/input/hog-lib.c
> > @@ -946,7 +946,7 @@ static void uhid_create(struct bt_hog *hog, uint8_t *report_map,
> >         struct uhid_event ev;
> >         ssize_t vlen = report_map_len;
> >         char itemstr[20]; /* 5x3 (data) + 4 (continuation) + 1 (null) */
> > -       int i, err;
> > +       int i, err, collection_depth = 0;
> >         GError *gerr = NULL;
> >
> >         DBG("Report MAP:");
> > @@ -960,6 +960,14 @@ static void uhid_create(struct bt_hog *hog, uint8_t *report_map,
> >                         if (!long_item && (value[i] & 0xfc) == 0x84)
> >                                 hog->has_report_id = TRUE;
> >
> > +                       // Start Collection
> > +                       if (value[i] == 0xa1)
> > +                               collection_depth++;
> > +
> > +                       // End Collection
> > +                       if (value[i] == 0xc0)
> > +                               collection_depth--;
> > +
> >                         DBG("\t%s", item2string(itemstr, &value[i], ilen));
> >
> >                         i += ilen;
> > @@ -968,10 +976,15 @@ static void uhid_create(struct bt_hog *hog, uint8_t *report_map,
> >
> >                         /* Just print remaining items at once and break */
> >                         DBG("\t%s", item2string(itemstr, &value[i], vlen - i));
> > -                       break;
> > +                       return;
> >                 }
> >         }
> >
> > +       if (collection_depth != 0) {
> > +               error("Report Map error: unbalanced collection");
> > +               return;
> > +       }
> > +
> >         /* create uHID device */
> >         memset(&ev, 0, sizeof(ev));
> >         ev.type = UHID_CREATE;
> > @@ -1365,7 +1378,9 @@ static void foreach_hog_chrc(struct gatt_db_attribute *attr, void *user_data)
> >                          * UHID to optimize reconnection.
> >                          */
> >                         uhid_create(hog, report_map.value, report_map.length);
> > -               } else {
> > +               }
> > +
> > +               if (!hog->uhid_created) {
> >                         read_char(hog, hog->attrib, value_handle,
> >                                                 report_map_read_cb, hog);
> >                 }
> > --
> > 2.29.2
> >
>
>
> --
> Luiz Augusto von Dentz