[Why]
Found kernel NULL pointer dereference under the below situation:
src — HDMI_Monitor src — HDMI_Monitor
e.g.: \ =>
MSTB — MSTB (unplug) MSTB — MSTB
When display 1 HDMI and 2 DP daisy chain monitors, unplugging the dp
cable connected to source causes kernel NULL pointer dereference at
drm_dp_mst_atomic_check_bw_limit(). When calculating pbn_limit, if
branch is null, accessing "&branch->ports" causes the problem.
[How]
Judge branch is null or not at the beginning. If it is null, return 0.
Signed-off-by: Wayne Lin <Wayne.Lin@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/gpu/drm/drm_dp_mst_topology.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 7d2d31eaf003..a6473e3ab448 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -4707,6 +4707,9 @@ int drm_dp_mst_atomic_check_bw_limit(struct drm_dp_mst_branch *branch,
struct drm_dp_vcpi_allocation *vcpi;
int pbn_limit = 0, pbn_used = 0;
+ if (!branch)
+ return 0;
+
list_for_each_entry(port, &branch->ports, next) {
if (port->mstb)
if (drm_dp_mst_atomic_check_bw_limit(port->mstb, mst_state))
--
2.17.1
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