drm/amdgpu: validate CP_GFX_SHADOW chunk size in CS pass1

commit 84c4c36 upstream.

Add a minimum-length check for the AMDGPU_CHUNK_ID_CP_GFX_SHADOW chunk in
amdgpu_cs_pass1(), matching the gate already present for the IB, FENCE and
BO_HANDLES chunk types.

The CP_GFX_SHADOW case previously shared a bare break with the dependency
and syncobj chunk types, which do not dereference a fixed-size struct. When
userspace submits this chunk with length_dw == 0, vmemdup_array_user() is
called with size 0 and returns ZERO_SIZE_PTR, which passes the IS_ERR()
check. amdgpu_cs_p2_shadow() then dereferences chunk->kdata as a struct
drm_amdgpu_cs_chunk_cp_gfx_shadow (reading shadow->flags), faulting on the
ZERO_SIZE_PTR and causing a NULL-pointer dereference.

This is reachable by an unprivileged process in the render group. Reject
undersized chunks with -EINVAL during pass1 so the bad submission is
rejected before pass2 ever dereferences the data.

Fixes: ac92870 ("drm/amdgpu: add gfx shadow CS IOCTL support")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7f61b2e)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: superm1

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -272,13 +272,17 @@ static int amdgpu_cs_pass1(struct amdgpu_cs_parser *p,
 				goto free_partial_kdata;
 			break;
 
+		case AMDGPU_CHUNK_ID_CP_GFX_SHADOW:
+			if (size < sizeof(struct drm_amdgpu_cs_chunk_cp_gfx_shadow))
+				goto free_partial_kdata;
+			break;
+
 		case AMDGPU_CHUNK_ID_DEPENDENCIES:
 		case AMDGPU_CHUNK_ID_SYNCOBJ_IN:
 		case AMDGPU_CHUNK_ID_SYNCOBJ_OUT:
 		case AMDGPU_CHUNK_ID_SCHEDULED_DEPENDENCIES:
 		case AMDGPU_CHUNK_ID_SYNCOBJ_TIMELINE_WAIT:
 		case AMDGPU_CHUNK_ID_SYNCOBJ_TIMELINE_SIGNAL:
-		case AMDGPU_CHUNK_ID_CP_GFX_SHADOW:
 			break;
 
 		default: