CVE-2021-47649 udmabuf: validate ubuf->pagecount

In the Linux kernel, the following vulnerability has been resolved: udmabuf: validate ubuf-pagecount Syzbot has reported GPF in sgallocappendtablefrompages. The problem was in ubuf-pages == ZEROPTR. ubuf-pagecount is calculated from arguments passed from user-space. If user creates udmabuf with...