On Tue, Nov 30, 2021 at 09:23:28PM +0800, Zhou Qingyang wrote:
> In cdv_intel_dp_get_modes(), the third return value of
> drm_mode_duplicate() is assigned to mode and used in
> drm_mode_probed_add(). drm_mode_probed_add() passes mode->head to
> list_add_tail(). list_add_tail() will further call __list_add() and
> there is a dereference of mode->head in __list_add(), which could lead
> to a wild pointer dereference on failure of drm_mode_duplicate().
>
> Fix this bug by adding a check of mode.
>
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
>
> Builds with CONFIG_DRM_GMA500=m show no new warnings,
> and our static analyzer no longer warns about this code.
>
> Fixes: d112a8163f83 ("gma500/cdv: Add eDP support")
> Signed-off-by: Zhou Qingyang <zhou1615@xxxxxxx>
> ---
> drivers/gpu/drm/gma500/cdv_intel_dp.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/gma500/cdv_intel_dp.c b/drivers/gpu/drm/gma500/cdv_intel_dp.c
> index ba6ad1466374..b389008965a9 100644
> --- a/drivers/gpu/drm/gma500/cdv_intel_dp.c
> +++ b/drivers/gpu/drm/gma500/cdv_intel_dp.c
> @@ -1773,6 +1773,9 @@ static int cdv_intel_dp_get_modes(struct drm_connector *connector)
> if (intel_dp->panel_fixed_mode != NULL) {
> struct drm_display_mode *mode;
> mode = drm_mode_duplicate(dev, intel_dp->panel_fixed_mode);
> + if (!mode)
> + return -ENOMEM;
.get_modes() isn't supposed to return negative values.
> +
> drm_mode_probed_add(connector, mode);
> return 1;
> }
> --
> 2.25.1
--
Ville Syrjälä
Intel
