drm/amdgpu: check amdgpu_vm_bo_find() result in GET_MAPPING_INFO

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: check amdgpu_vm_bo_find() result in GET_MAPPING_INFO The AMDGPU_GEM_OP_GET_MAPPING_INFO path of amdgpu_gem_op_ioctl() looks up the bo_va for the buffer object in the caller's VM via amdgpu_vm_bo_find(), but uses the returned pointer without checking it. amdgpu_vm_bo_find() returns NULL when the BO has no bo_va in that VM, which is the normal case for a BO that has never been mapped. The result is fed straight into amdgpu_vm_bo_va_for_each_valid_mapping(), which expands to list_for_each_entry(mapping, &(bo_va)->valids, list) and dereferences bo_va, causing a NULL pointer dereference. This is reachable by any process able to issue the ioctl (render group) simply by requesting mapping info for an unmapped BO. Return -ENOENT when no bo_va is found, jumping to out_exec so the drm_exec context and GEM object reference are released. (cherry picked from commit 528b19377affc1cc7362a70a254c1dda793595f9)