On Fri, Apr 16, 2021 at 05:58:25PM +0200, Christian Brauner wrote:
> On Fri, Apr 16, 2021 at 03:35:59PM +0000, Al Viro wrote:
> > On Fri, Apr 16, 2021 at 05:13:10PM +0200, Christian Brauner wrote:
> >
> > > My point here was more that the _file_ has already been opened _before_
> > > that call to io_uring_add_task_file(). But any potential non-trivial
> > > side-effects of opening that file that you correctly pointed out in an
> > > earlier mail has already happened by that time.
> >
> > The file comes from io_uring_get_file(), the entire thing is within the
> > io_ring_ctx constructor and the only side effect there is ->ring_sock
> > creation. And that stays until the io_ring_ctx is freed. I'm _not_
> > saying I like io_uring style in general, BTW - in particular,
> > ->ring_sock->file handling is a kludge (as is too much of interation
> > with AF_UNIX machinery there). But from side effects POV we are fine
> > there.
> >
> > > Granted there are more
> > > obvious examples, e.g. the binder stuff.
> > >
> > > int fd = get_unused_fd_flags(O_CLOEXEC);
> > >
> > > if (fd < 0) {
> > > binder_debug(BINDER_DEBUG_TRANSACTION,
> > > "failed fd fixup txn %d fd %d\n",
> > > t->debug_id, fd);
> > > ret = -ENOMEM;
> > > break;
> > > }
> > > binder_debug(BINDER_DEBUG_TRANSACTION,
> > > "fd fixup txn %d fd %d\n",
> > > t->debug_id, fd);
> > > trace_binder_transaction_fd_recv(t, fd, fixup->offset);
> > > fd_install(fd, fixup->file);
> > > fixup->file = NULL;
> > > if (binder_alloc_copy_to_buffer(&proc->alloc, t->buffer,
> > > fixup->offset, &fd,
> > > sizeof(u32))) {
> > > ret = -EINVAL;
> > > break;
> > > }
> >
> > ... and it's actually broken, since this
> > /* All copies must be 32-bit aligned and 32-bit size */
> > if (!check_buffer(alloc, buffer, buffer_offset, bytes))
> > return -EINVAL;
> > in binder_alloc_copy_to_buffer() should've been done *before*
> > fd_install(). If anything, it's an example of the situation when
> > fd_receive() would be wrong...
>
> They could probably refactor this but I'm not sure why they'd bother. If
> they fail processing any of those files they end up aborting the
> whole transaction.
> (And the original code didn't check the error code btw.)
(dma_buf_fd() seems like another good candidate. But again, I don't have
any plans to shove this down anyone's throat.)
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