mm/gup_benchmark.c: prevent integer overflow in ioctl

mainline inclusion
from mainline-4.20-rc1
commit 4b408c74ee5a0b74fc9265c2fe39b0e7dec7c056
category: bugfix
bugzilla: 5946
CVE: NA

----------------------------

The concern here is that "gup->size" is a u64 and "nr_pages" is unsigned
long.  On 32 bit systems we could trick the kernel into allocating fewer
pages than expected.

Link: http://lkml.kernel.org/r/20181025061546.hnhkv33diogf2uis@kili.mountain
Fixes: 64c349f4 ("mm: add infrastructure for get_user_pages_fast() benchmarking")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NJing xiangfeng <jingxiangfeng@huawei.com>
Reviewed-by: Nzhongjiang <zhongjiang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

mm/gup_benchmark.c

@@ -23,6 +23,9 @@ static int __gup_benchmark_ioctl(unsigned int cmd,
 	int nr;
 	struct page **pages;
 
+	if (gup->size > ULONG_MAX)
+		return -EINVAL;
+
 	nr_pages = gup->size / PAGE_SIZE;
 	pages = kvcalloc(nr_pages, sizeof(void *), GFP_KERNEL);
 	if (!pages)