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 Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com --- 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.

Changes in v2: - Added a comment/changed math to help make it easier to grok.

drivers/gpu/drm/drm_edid.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 9c9463ec5465..0383d97c306f 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -1840,11 +1840,20 @@ static void connector_bad_edid(struct drm_connector *connector, u8 *edid, int num_blocks) { int i; - u8 num_of_ext = edid[0x7e]; + u8 last_block; + + /* + * 0x7e in the EDID is the number of extension blocks. The EDID + * is 1 (base block) + num_ext_blocks big. That means we can think + * of 0x7e in the EDID of the _index_ of the last block in the + * combined chunk of memory. + */ + last_block = 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 (last_block < num_blocks) + connector->real_edid_checksum = + drm_edid_block_checksum(edid + last_block * EDID_LENGTH);

if (connector->bad_edid_counter++ && !drm_debug_enabled(DRM_UT_KMS)) return;