[PATCH 6/9] drm/udl: Return error if vendor descriptor is too short

[Patrik Jakobsson]

On Thu, Apr 3, 2025 at 9:28 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Hi
>
> Am 02.04.25 um 15:16 schrieb Patrik Jakobsson:
> > On Tue, Apr 1, 2025 at 6:23 PM Thomas Zimmermann <tzimmermann at suse.de> wrote:
> >> There need to be least 5 bytes in the vendor descriptor. Return
> >> an error otherwise. Also change the branching to early-out on
> >> the error. Adjust indention of the rest of the parser function.
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> >> ---
> >>   drivers/gpu/drm/udl/udl_main.c | 72 +++++++++++++++++-----------------
> >>   1 file changed, 36 insertions(+), 36 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/udl/udl_main.c b/drivers/gpu/drm/udl/udl_main.c
> >> index 4291ddb7158c4..58d6065589d3a 100644
> >> --- a/drivers/gpu/drm/udl/udl_main.c
> >> +++ b/drivers/gpu/drm/udl/udl_main.c
> >> @@ -45,43 +45,43 @@ static int udl_parse_vendor_descriptor(struct udl_device *udl)
> >>                  goto unrecognized;
> >>          len = ret;
> >>
> >> -       if (len > 5) {
> >> -               DRM_INFO("vendor descriptor length: %u data:%11ph\n",
> >> -                        len, desc);
> >> -
> >> -               if ((desc[0] != len) ||    /* descriptor length */
> >> -                   (desc[1] != 0x5f) ||   /* vendor descriptor type */
> >> -                   (desc[2] != 0x01) ||   /* version (2 bytes) */
> >> -                   (desc[3] != 0x00) ||
> >> -                   (desc[4] != len - 2))  /* length after type */
> >> -                       goto unrecognized;
> >> -
> >> -               desc_end = desc + len;
> >> -               desc += 5; /* the fixed header we've already parsed */
> >> -
> >> -               while (desc < desc_end) {
> >> -                       u8 length;
> >> -                       u16 key;
> >> -
> >> -                       key = le16_to_cpu(*((u16 *) desc));
> >> -                       desc += sizeof(u16);
> >> -                       length = *desc;
> >> -                       desc++;
> >> -
> >> -                       switch (key) {
> >> -                       case 0x0200: { /* max_area */
> >> -                               u32 max_area;
> >> -                               max_area = le32_to_cpu(*((u32 *)desc));
> >> -                               DRM_DEBUG("DL chip limited to %d pixel modes\n",
> >> -                                       max_area);
> >> -                               udl->sku_pixel_limit = max_area;
> >> -                               break;
> >> -                       }
> >> -                       default:
> >> -                               break;
> >> -                       }
> >> -                       desc += length;
> >> +       if (len < 5)
> > Hi Thomas,
> >
> > Shouldn't this be if (len <= 5)? The old code only parsed if the
> > descriptor returned at least 6 bytes.
>
> Right, I also noticed that. But I though it was a mistake. The header is
> 5 bytes and if there are no key-value pairs it's still a valid
> descriptor AFAICT. Patch 9 of the series sets a default for the pixel
> limit and the adapter would be usable. I rather not change the new
> logic, but add an explanation to the commit description. Ok?

Sounds good. With that and the small fix in patch 9/9 everything else
looks fine.

With the mentioned fixes done:
Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson at gmail.com>

>
> Best regards
> Thomas
>
> >
> > -Patrik
> >
> >> +               goto unrecognized;
> >> +
> >> +       DRM_INFO("vendor descriptor length: %u data:%11ph\n", len, desc);
> >> +
> >> +       if ((desc[0] != len) ||    /* descriptor length */
> >> +           (desc[1] != 0x5f) ||   /* vendor descriptor type */
> >> +           (desc[2] != 0x01) ||   /* version (2 bytes) */
> >> +           (desc[3] != 0x00) ||
> >> +           (desc[4] != len - 2))  /* length after type */
> >> +               goto unrecognized;
> >> +
> >> +       desc_end = desc + len;
> >> +       desc += 5; /* the fixed header we've already parsed */
> >> +
> >> +       while (desc < desc_end) {
> >> +               u8 length;
> >> +               u16 key;
> >> +
> >> +               key = le16_to_cpu(*((u16 *)desc));
> >> +               desc += sizeof(u16);
> >> +               length = *desc;
> >> +               desc++;
> >> +
> >> +               switch (key) {
> >> +               case 0x0200: { /* max_area */
> >> +                       u32 max_area = le32_to_cpu(*((u32 *)desc));
> >> +
> >> +                       DRM_DEBUG("DL chip limited to %d pixel modes\n",
> >> +                                 max_area);
> >> +                       udl->sku_pixel_limit = max_area;
> >> +                       break;
> >> +               }
> >> +               default:
> >> +                       break;
> >>                  }
> >> +               desc += length;
> >>          }
> >>
> >>          goto success;
> >> --
> >> 2.49.0
> >>
>
> --
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Frankenstrasse 146, 90461 Nuernberg, Germany
> GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
> HRB 36809 (AG Nuernberg)
>