On Tue, Sep 20, 2016 at 1:38 PM, Al Viro <v...@zeniv.linux.org.uk> wrote: > > Not the point. Of course it *would* fail; the problem is that the loop > that would ping each page is never executed.
You're missing the point. If "access_ok()" is fine with wrapping, then some otehr system call that wraps will successfully do a memcpy_from/to_user() with a wrapped address (and the proper mappings). Which is completely bogus. So access_ok() should be fixed regardless. An access_ok() that accepts a wrapping address is a bug. End of story. And once that bug is fixed, the fault_in_multipages..() issue is moot. So it shouldn't be an issue. Linus