[PATCH] drm/amd/display: Add sanity checks for drm_edid_raw()

[Takashi Iwai <tiwai@suse.de>]

When EDID is retrieved via drm_edid_raw(), it doesn't guarantee to
return proper EDID bytes the caller wants: it may be either NULL (that
leads to an Oops) or with too long bytes over the fixed size raw_edid
array (that may lead to memory corruption).  The latter was reported
actually when connected with a bad adapter.

Add sanity checks for drm_edid_raw() to address the above corner
cases, and return EDID_BAD_INPUT accordingly.

Fixes: 48edb2a4256e ("drm/amd/display: switch amdgpu_dm_connector to use struct drm_edid")
Link: https://bugzilla.suse.com/show_bug.cgi?id=1236415
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---

BTW, I'm not sure why memmove() is used instead of memcpy().
I left as is for now.

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c  | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
index fbd80d8545a8..a92bc12a095e 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
@@ -980,6 +980,7 @@ enum dc_edid_status dm_helpers_read_local_edid(
 	enum dc_edid_status edid_status;
 	const struct drm_edid *drm_edid;
 	const struct edid *edid;
+	size_t edid_len;
 
 	if (link->aux_mode)
 		ddc = &aconnector->dm_dp_aux.aux.ddc;
@@ -1010,8 +1011,13 @@ enum dc_edid_status dm_helpers_read_local_edid(
 			return EDID_NO_RESPONSE;
 
 		edid = drm_edid_raw(drm_edid); // FIXME: Get rid of drm_edid_raw()
-		sink->dc_edid.length = EDID_LENGTH * (edid->extensions + 1);
-		memmove(sink->dc_edid.raw_edid, (uint8_t *)edid, sink->dc_edid.length);
+		if (!edid)
+			return EDID_BAD_INPUT;
+		edid_len = EDID_LENGTH * (edid->extensions + 1);
+		if (edid_len > sizeof(sink->dc_edid.raw_edid))
+			return EDID_BAD_INPUT;
+		sink->dc_edid.length = edid_len;
+		memmove(sink->dc_edid.raw_edid, (uint8_t *)edid, edid_len);
 
 		/* We don't need the original edid anymore */
 		drm_edid_free(drm_edid);
-- 
2.43.0