[HEADSUP] Disallowing read() of a directory fd

[Warner Losh]

On Thu, May 14, 2020, 7:14 PM Arne Steinkamm <freebsd-arch at steinkamm.com>
wrote:

> On Thu, May 14, 2020 at 02:20:45PM -0600, Alan Somers wrote:
> > On Thu, May 14, 2020 at 2:17 PM Julian H. Stacey <jhs at berklix.com>
> wrote:
> >
> > > Kyle Evans wrote:
> > > > Hi,
> > > >
> > > > This is a heads up, given that I'm completely flipping our historical
> > > > behavior- I intend to commit this review in a couple days' time
> > > > without substantial objection: https://reviews.freebsd.org/D24596
> > > >
> > > > With this, FreeBSD 13 will not allow read() of a directory fd, which
> > > > could have previously returned some data from the underlying
> > > > filesystem in no particular standardized format.
> > > >
> > > > This is a still-standards-compliant switch from one
> > > > implementation-defined behavior to another that's already been
> adopted
> > > > in various other popular kernels, to include OpenBSD, MacOS, and
> > > > Linux.
> > > >
> > > > Worth noting is that there's not really one largely-compelling
> reasons
> > > > to switch this after so many years (unless you find yourself that
> > > > irate when you accidentally `cat` a directory), but there are some
> > > > benefits which are briefly discussed in the commentary around the
> > > > review along with the history of the current behavior.
> > > >
> > > > This change also simplifies filesystem implementations to some
> extent.
> > > >
> > > > Thanks,
> > > >
> > > > Kyle Evans
> > >
> > > There is ZERO need for a spurious change at 2 days notice after 42+
> years !
> > >
> > > "cat ." as been supported since Unix V6 1978 or earlier,
> > > no problem, even occasionaly useful.
> > >
> >
> > Really?  When is that occasionally useful?  I've never seen anything
> useful
> > come out of reading a directory.
>
> It's all about files in Unix...
>
> This is true since 1972.
>
> And files can be read!
>
> How many (bad programmed) shell scripts will break when directory files
> can't
> be read anymore? I have no idea.
>
> But I know for sure that there is no need to make this change.
> Not 1976, not 2020 nor in the future


Why do you need this to work? It can disclose unwanted data...

Warner

.//. Arne
>
> --
> Arne Steinkamm         | Home:     Mail: arne<at>steinkamm<dot>com
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