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
