On Sat, 9 Jun 2007, Davide Libenzi wrote:
> On Sat, 9 Jun 2007, Al Viro wrote:
>
> > That's simply not true. On the current kernel nothing stops you from e.g.
> > picking a random number and using F_DUPFD. Voila - there's your randomized
> > descriptor. Portable to earlier kernels.
> >
> > Moreover, nonsense^H^H^Hq_fd() can be implemented in userland just fine
> > if we allow F_DUPFD to arbitrary number - just pass it a random one *or*
> > base chosen like davedel is doing (constant + 20bit random chosen at start
> > time).
>
> That does not work. Or better, it works but it forces *huge* fdtables to
> be created. To do that, you need "start" to be over NR_FILE, and this
> creates an fdtable bigger than NR_FILE ((pointer-size + a-few-bits) *
> NR_FILE) propagated down to every app you fork.
Keep in mind also, that quite a few places in the code, walk through the
whole fdtable memory. So it is not only a problem of wasted RAM.
- Davide
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