hugetlbfs: fix bug in pgoff overflow checking

This is a fix for a regression in 32 bit kernels caused by an invalid
check for pgoff overflow in hugetlbfs mmap setup.  The check incorrectly
specified that the size of a loff_t was the same as the size of a long.
The regression prevents mapping hugetlbfs files at offsets greater than
4GB on 32 bit kernels.

On 32 bit kernels conversion from a page based unsigned long can not
overflow a loff_t byte offset.  Therefore, skip this check if
sizeof(unsigned long) != sizeof(loff_t).

Link: http://lkml.kernel.org/r/20180330145402.5053-1-mike.kravetz@oracle.com
Fixes: 63489f8e ("hugetlbfs: check for pgoff value overflow")
Reported-by: NDan Rue <dan.rue@linaro.org>
Signed-off-by: NMike Kravetz <mike.kravetz@oracle.com>
Tested-by: NAnders Roxell <anders.roxell@linaro.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Nic Losby <blurbdust@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/hugetlbfs/inode.c

@@ -138,10 +138,14 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
 
 	/*
 	 * page based offset in vm_pgoff could be sufficiently large to
-	 * overflow a (l)off_t when converted to byte offset.
+	 * overflow a loff_t when converted to byte offset.  This can
+	 * only happen on architectures where sizeof(loff_t) ==
+	 * sizeof(unsigned long).  So, only check in those instances.
 	 */
+	if (sizeof(unsigned long) == sizeof(loff_t)) {
 		if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
 			return -EINVAL;
+	}
 
 	/* must be huge page aligned */
 	if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))