On Tue, Oct 10, 2023 at 05:55:04PM +0100, Al Viro wrote: > On Tue, Oct 10, 2023 at 03:34:45PM +0200, Miklos Szeredi wrote: > > On Tue, 10 Oct 2023 at 15:17, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > > Sorry, you asked about ovl mount. > > > To me it makes sense that if users observe ovl paths in writable mapped > > > memory, that ovl should not be remounted RO. > > > Anyway, I don't see a good reason to allow remount RO for ovl in that case. > > > Is there? > > > > Agreed. > > > > But is preventing remount RO important enough to warrant special > > casing of backing file in generic code? I'm not convinced either > > way... > > You definitely want to guarantee that remounting filesystem r/o > prevents the changes of visible contents; it's not just POSIX, > it's a fairly basic common assumption about any local filesystems. Incidentally, could we simply keep a reference to original struct file instead of messing with path? The only caller of backing_file_open() gets &file->f_path as user_path; how about passing file instead, and having backing_file_open() do get_file() on it and stash the sucker into your object? And have put_file_access() do if (unlikely(file->f_mode & FMODE_BACKING)) fput(backing_file(file)->file); in the end. No need to mess with write access in any special way and it's closer to the semantics we have for normal mmap(), after all - it keeps the file we'd passed to it open as long as mapping is there. Comments?
