Repost: Missing security_mmap_file() in remap_file_pages syscall

[Kirill A. Shutemov]

On Mon, Mar 25, 2019 at 01:33:51PM -0400, TongZhang wrote:
> Dear Kernel Developers,
> 
> We’d like to bring this up for a discussion again.
> 
> Several months ago we posted an email discussing a case where remap_file_pages() has no security_mmap_file() check.
> At that time we were told that do_mmap_pgoff() will base the new VMA permission on the old one.
> But somehow we still think the check is needed, for the reason that the advisory could first do a 
> mmap() which can pass SELinux check then remap using a completely different file or region of file,
> which could possibly pose a risk.

Could you elabarote on the risk you see? A bad scenario that could be
prevented with SELinux check would be helpful.

-- 
 Kirill A. Shutemov