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@linux.intel.com Signed-off-by: Douglas Anderson dianders@chromium.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@linux.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