As drm_dp_get_mst_branch_device_by_guid() is called from drm_dp_get_mst_branch_device_by_guid(), mstb parameter has to be checked, otherwise NULL dereference may occur in the call to the memcpy() and cause following:
[12579.365869] BUG: kernel NULL pointer dereference, address: 0000000000000049 [12579.365878] #PF: supervisor read access in kernel mode [12579.365880] #PF: error_code(0x0000) - not-present page [12579.365882] PGD 0 P4D 0 [12579.365887] Oops: 0000 [#1] PREEMPT SMP NOPTI ... [12579.365895] Workqueue: events_long drm_dp_mst_up_req_work [12579.365899] RIP: 0010:memcmp+0xb/0x29 [12579.365921] Call Trace: [12579.365927] get_mst_branch_device_by_guid_helper+0x22/0x64 [12579.365930] drm_dp_mst_up_req_work+0x137/0x416 [12579.365933] process_one_work+0x1d0/0x419 [12579.365935] worker_thread+0x11a/0x289 [12579.365938] kthread+0x13e/0x14f [12579.365941] ? process_one_work+0x419/0x419 [12579.365943] ? kthread_blkcg+0x31/0x31 [12579.365946] ret_from_fork+0x1f/0x30
As get_mst_branch_device_by_guid_helper() is recursive, moving condition to the first line allow to remove a similar one for step over of NULL elements inside a loop.
Fixes: 5e93b8208d3c ("drm/dp/mst: move GUID storage from mgr, port to only mst branch") Cc: stable@vger.kernel.org # 4.14+ Signed-off-by: Lukasz Majczak lma@semihalf.com Reviewed-by: Radoslaw Biernacki rad@chromium.org Signed-off-by: Manasi Navare navaremanasi@chromium.org Link: https://patchwork.freedesktop.org/patch/msgid/20230922063410.23626-1-lma@sem... (cherry picked from commit 3d887d512494d678b17c57b835c32f4e48d34f26) Signed-off-by: Lukasz Majczak lma@semihalf.com --- drivers/gpu/drm/drm_dp_mst_topology.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 64faa70a9dd9..879638e6bea4 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -1268,14 +1268,14 @@ static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper( struct drm_dp_mst_branch *found_mstb; struct drm_dp_mst_port *port;
+ if (!mstb) + return NULL; + if (memcmp(mstb->guid, guid, 16) == 0) return mstb;
list_for_each_entry(port, &mstb->ports, next) { - if (!port->mstb) - continue; - found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
if (found_mstb)