On 30/11/2021 14:25, Zhou Qingyang wrote:
In komeda_plane_add(), komeda_get_layer_fourcc_list() is assigned to formats and used in drm_universal_plane_init(). drm_universal_plane_init() passes formats to __drm_universal_plane_init(). __drm_universal_plane_init() further passes formats to memcpy() as src parameter, which could lead to an undefined behavior bug on failure of komeda_get_layer_fourcc_list().
Fix this bug by adding a check of formats.
This bug was found by a static analyzer. The analysis employs differential checking to identify inconsistent security operations (e.g., checks or kfrees) between two code paths and confirms that the inconsistent operations are not recovered in the current function or the callers, so they constitute bugs.
Note that, as a bug found by static analysis, it can be a false positive or hard to trigger. Multiple researchers have cross-reviewed the bug.
Builds with CONFIG_DRM_KOMEDA=m show no new warnings, and our static analyzer no longer warns about this code.
Fixes: 61f1c4a8ab75 ("drm/komeda: Attach komeda_dev to DRM-KMS") Signed-off-by: Zhou Qingyang zhou1615@umn.edu
drivers/gpu/drm/arm/display/komeda/komeda_plane.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c index d63d83800a8a..dd3f17e970dd 100644 --- a/drivers/gpu/drm/arm/display/komeda/komeda_plane.c +++ b/drivers/gpu/drm/arm/display/komeda/komeda_plane.c @@ -265,6 +265,10 @@ static int komeda_plane_add(struct komeda_kms_dev *kms,
formats = komeda_get_layer_fourcc_list(&mdev->fmt_tbl, layer->layer_type, &n_formats);
- if (!formats) {
err = -ENOMEM;goto cleanup;- }
If this executes it will cause undefined behaviour...
The cleanup code calls komeda_plane_destroy() which calls drm_plane_cleanup() which does (amongst other things) a list_del(&plane->head). But the plane hasn't been put on a list yet as that's done in drm_universal_plane_init().
So in this case we simple want to do:
if (!formats) { kfree(kplane); return -ENOMEM; }
Note that without this 'fix' a NULL return from komeda_get_layer_fourcc_list() would leave n_formats==0, so while the NULL pointer is passed into memcpy() it is also passed a length of 0. Which I believe is safe.
However while looking at this function...
err = drm_universal_plane_init(&kms->base, plane, get_possible_crtcs(kms, c->pipeline),
This call to drm_universal_plane_init() can fail early before plane->head has been initialised. In which case the following:
komeda_put_fourcc_list(formats);
if (err) goto cleanup;
commits the exact same sin and would cause a similar NULL dereference in drm_plane_cleanup().
Steve