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    Subject[PATCH 5.10 089/103] drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read
    Date
    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
    @@ -1835,11 +1835,20 @@ 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;

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