A vma with vm_pgoff large enough to overflow a loff_t type when
converted to a byte offset can be passed via the remap_file_pages
system call.  The hugetlbfs mmap routine uses the byte offset to
calculate reservations and file size.

A sequence such as:
  mmap(0x20a00000, 0x600000, 0, 0x66033, -1, 0);
  remap_file_pages(0x20a00000, 0x600000, 0, 0x20000000000000, 0);
will result in the following when task exits/file closed,
  kernel BUG at mm/hugetlb.c:749!
Call Trace:

The overflowed pgoff value causes hugetlbfs to try to set up a
mapping with a negative range (end < start) that leaves invalid
state which causes the BUG.

Reported-by: Nic Losby <blurbd...@gmail.com>
Signed-off-by: Mike Kravetz <mike.krav...@oracle.com>
 fs/hugetlbfs/inode.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 8fe1b0aa2896..cb288dec5564 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -127,12 +127,13 @@ static int hugetlbfs_file_mmap(struct file *file, struct 
vm_area_struct *vma)
        vma->vm_ops = &hugetlb_vm_ops;
-        * Offset passed to mmap (before page shift) could have been
-        * negative when represented as a (l)off_t.
+        * page based offset in vm_pgoff could be sufficiently large to
+        * overflow a (l)off_t when converted to byte offset.
-       if (((loff_t)vma->vm_pgoff << PAGE_SHIFT) < 0)
+       if (vma->vm_pgoff && ((loff_t)vma->vm_pgoff << PAGE_SHIFT) <= 0)
                return -EINVAL;
+       /* must be huge page aligned */
        if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
                return -EINVAL;

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