[PATCH 5.14 126/151] drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read

Greg Kroah-Hartman
2021-10-18T14:00:15Z

From: Douglas Anderson <dianders@chromium.org>

commit 97794170b696856483f74b47bfb6049780d2d3a0 upstream.

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>
Link: https://patchwork.freedesktop.org/patch/msgid/20211005192905.v2.1.Ib059f9c23c2611cb5a9d760e7d0a700c1295928d@changeid
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/drm_edid.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1834,11 +1834,20 @@ static void connector_bad_edid(struct dr
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;