On Mon, Nov 27, 2023 at 09:10:54AM -0800, Linus Torvalds wrote: > On Mon, 27 Nov 2023 at 02:27, Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > > So I've picked up your patch (vfs.misc). It's clever alright so thanks > > for the comments in there otherwise I would've stared at this for far > > too long. > > Note that I should probably have commented on one other thing: that > whole "just load from fd[0] is always safe, because the fd[] array > always exists". I added a comment to that effect in the code. > > IOW, that whole "load and mask" thing only works when you know the > array exists at all. > > Doing that "just mask the index" wouldn't be valid if "size = 0" is an > option and might mean that we don't have an array at all (ie if "->fd" > itself could be NULL. > > But we never have a completely empty file descriptor array, and > fdp->fd is never NULL. At a minimum 'max_fds' is NR_OPEN_DEFAULT. > > (The whole 'tsk->files' could be NULL, but only for kernel threads or > when exiting, so fget_task() will check for *that*, but it's a > separate thing) Yep. > > So that's why it's safe to *entirely* remove the whole > > if (unlikely(fd >= fdt->max_fds)) > > test, and do it *all* with just "mask the index, and mask the resulting load". Yep.
