On Mon, Oct 30, 2023 at 12:29:04PM +0100, Lukasz Majczak wrote: > 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@xxxxxxxxxxxxxxx> # 4.14+ > Signed-off-by: Lukasz Majczak <lma@xxxxxxxxxxxx> > Reviewed-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx> > Signed-off-by: Manasi Navare <navaremanasi@xxxxxxxxxxxx> > Link: https://patchwork.freedesktop.org/patch/msgid/20230922063410.23626-1-lma@xxxxxxxxxxxx > (cherry picked from commit 3d887d512494d678b17c57b835c32f4e48d34f26) > Signed-off-by: Lukasz Majczak <lma@xxxxxxxxxxxx> > --- > drivers/gpu/drm/drm_dp_mst_topology.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > All now queued up, thanks. greg k-h