Messages in this thread |  | | Date | Sun, 30 Oct 2016 10:44:37 +0100 | From | Jan Kara <> | Subject | Re: [PATCH] aio: fix a user triggered use after free (and fix freeze protection of aio writes) |
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On Sat 29-10-16 13:09:25, Linus Torvalds wrote: > On Sat, Oct 29, 2016 at 12:17 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > AFAICS, the possibility of dropping the last reference to struct file > > before ->write_iter() has returned is fundamentally broken. I might be > > missing something subtle here, but... > > Ok, let's add a get_file(); fput(); around that whole iter call sequence. > > And that's a separate issue from "we should hold the fs freezer lock > around the whole operation". So I think we need both.
Yup, these are two separate issues. I'm fine with adding get_file(); fput() around the iter call sequence. Then, when we have struct file available for the whole time ->write_iter runs, I'd prefer to keep the call to fool lockdep where original file_end_write() call was - that gives us proper lockdep coverage for all the code behind iter_op(). The downside is we cannot keep helpers as elegant as you suggested in your patch but I believe it's bearable and worth the additional lockdep coverage. I'll send patches shortly...
Honza
-- Jan Kara <jack@suse.com> SUSE Labs, CR
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