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Date: Tue, 5 Oct 2021 18:46:39 +0300 From: Ville Syrjälä <ville.syrjala@...ux.intel.com> To: Douglas Anderson <dianders@...omium.org> Cc: dri-devel@...ts.freedesktop.org, Rodrigo.Siqueira@....com, Harry.Wentland@....com, khsieh@...eaurora.org, Jerry.Zuo@....com, alexander.deucher@....com, Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read On Tue, Oct 05, 2021 at 08:10:28AM -0700, Douglas Anderson wrote: > In commit e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid > corruption test") the function connector_bad_edid() started assuming > that the memory for the EDID passed to it was big enough to hold > `edid[0x7e] + 1` blocks of data (1 extra for the base block). It > completely ignored the fact that the function was passed `num_blocks` > which indicated how much memory had been allocated for the EDID. > > Let's fix this by adding a bounds check. > > This is important for handling the case where there's an error in the > first block of the EDID. In that case we will call > connector_bad_edid() without having re-allocated memory based on > `edid[0x7e]`. > > Fixes: e11f5bd8228f ("drm: Add support for DP 1.4 Compliance edid corruption test") > Reported-by: Ville Syrjälä <ville.syrjala@...ux.intel.com> > Signed-off-by: Douglas Anderson <dianders@...omium.org> > --- > This problem report came up in the context of a patch I sent out [1] > and this is my attempt at a fix. The problem predates my patch, > though. I don't personally know anything about DP compliance testing > and what should be happening here, nor do I apparently have any > hardware that actually reports a bad EDID. Thus this is just compile > tested. I'm hoping that someone here can test this and make sure it > seems OK to them. > > drivers/gpu/drm/drm_edid.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > index 9b19eee0e1b4..ccfa08631c57 100644 > --- a/drivers/gpu/drm/drm_edid.c > +++ b/drivers/gpu/drm/drm_edid.c > @@ -1843,8 +1843,9 @@ static void connector_bad_edid(struct drm_connector *connector, > u8 num_of_ext = edid[0x7e]; > > /* Calculate real checksum for the last edid extension block data */ > - connector->real_edid_checksum = > - drm_edid_block_checksum(edid + num_of_ext * EDID_LENGTH); > + if (num_of_ext <= num_blocks - 1) Something about that doesn't really agree with my brain. It's correct but when I read it I can't immediately see it. I guess what I'd like to see is something like: last_block = edid[0x7e]; if (last_block < num_blocks) connector->real_edid_checksum = drm_edid_block_checksum(edid + last_block * EDID_LENGTH); Techically exactly the same thing, but I don't have to read the comparison twice to convince myself that it's correct. Anyways, this is Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com> either way. > + connector->real_edid_checksum = > + drm_edid_block_checksum(edid + num_of_ext * EDID_LENGTH); > > if (connector->bad_edid_counter++ && !drm_debug_enabled(DRM_UT_KMS)) > return; > -- > 2.33.0.800.g4c38ced690-goog -- Ville Syrjälä Intel
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