Hi,

On 14/04/2022 09:14, Xiaomeng Tong wrote:

The bug is here: bus_flags = connector->display_info.bus_flags;

The list iterator 'connector-' will point to a bogus position containing HEAD if the list is empty or no element is found. This case must be checked before any use of the iterator, otherwise it will lead to a invalid memory access.

To fix this bug, add an check. Use a new value 'iter' as the list iterator, while use the old value 'connector' as a dedicated variable to point to the found element.

Cc: stable@vger.kernel.org Fixes: ("drm/omap: Add support for drm_panel") Signed-off-by: Xiaomeng Tong xiam0nd.tong@gmail.com

---

drivers/gpu/drm/omapdrm/omap_encoder.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/omap_encoder.c b/drivers/gpu/drm/omapdrm/omap_encoder.c index 4dd05bc732da..d648ab4223b1 100644 --- a/drivers/gpu/drm/omapdrm/omap_encoder.c +++ b/drivers/gpu/drm/omapdrm/omap_encoder.c @@ -76,14 +76,16 @@ static void omap_encoder_mode_set(struct drm_encoder *encoder, struct omap_encoder *omap_encoder = to_omap_encoder(encoder); struct omap_dss_device *output = omap_encoder->output; struct drm_device *dev = encoder->dev;

• struct drm_connector *connector;

• struct drm_connector *connector = NULL, *iter; struct drm_bridge *bridge; struct videomode vm = { 0 }; u32 bus_flags;

• list_for_each_entry(connector, &dev->mode_config.connector_list, head) {

• if (connector->encoder == encoder)
  

• list_for_each_entry(iter, &dev->mode_config.connector_list, head) {

• if (iter->encoder == encoder) {
  

• 	connector = iter;
  break;
  

• }
  

  }

When does this bug happen? How do you get omap_encoder_mode_set() called for an encoder with a connector that is not valid?

drm_display_mode_to_videomode(adjusted_mode, &vm); @@ -106,8 +108,10 @@ static void omap_encoder_mode_set(struct drm_encoder *encoder, omap_encoder_update_videomode_flags(&vm, bus_flags); }

• bus_flags = connector->display_info.bus_flags;
• omap_encoder_update_videomode_flags(&vm, bus_flags);

• if (connector) {

• bus_flags = connector->display_info.bus_flags;
  

• omap_encoder_update_videomode_flags(&vm, bus_flags);
  

• }

/* Set timings for all devices in the display pipeline. */ dss_mgr_set_timings(output, &vm);

How does this fix the issue? You just skip the lines that set up the videomode, but then pass that videomode to dss_mgr_set_timings()...

Tomi