Re: [RFC/PATCH] revoke/frevoke system calls V2

From: Horst H. von Brand
Date: Thu Jul 27 2006 - 15:29:39 EST

Pekka Enberg <penberg@xxxxxxxxxxxxxx> wrote:
> On Thu, 2006-07-27 at 20:06 +0200, Petr Baudis wrote:
> > Make that setuid root or just create log file owned by you and make root
> > run it. Should be innocent enough, right?
> >
> > Well, except that you can revoke the log file before the shadow file is
> > opened, at which point open() probably reuses the fd and the program
> > conveniently logs to /etc/shadow.

> No, the fd is leaked on purpose to avoid recycling. See revoke_fds for
> details.

Doesn't that violate a POSIX guarantee that the lowest unused fd is
returned? If the leakage lasts "long enough", this gives an opportunity of
a nice DoS by using up fds...
Dr. Horst H. von Brand User #22616
Departamento de Informatica Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria +56 32 654239
Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513

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