[HEADSUP] Disallowing read() of a directory fd

[Arne Steinkamm]

On Fri, May 15, 2020 at 10:48:15AM -0400, Diane Bruce wrote:
> All I have to say on this noisy bikeshed is, let's resurrect the mkdir
> bug of V7 because it's tradition and the BSD way and history and stuff.
> (I only expect a few of you to remember this one.)

Oh, this "bug" was alive until Sys V 3.2 times...

Implementing mkdir as library function without a syscall wasn't a good idea.
ken and dmr saw no reason to implement mkdir as atomic operation.
So it was easy, even with a shell script, to jump between the
mknod(2) and the chown(2) to replace the directory node with a symlink to
/etc/passwd.

This was from a todays point of view a stupid mistake. Reading a directory node
is lightyears away from "a stupid mistake".

Make it switchable with a sysctl switch... would be the best of both worlds.

.//. Arne

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