bug#12632: file permissions checking mishandled when setuid

[Paul Eggert]

On 10/20/2012 09:24 PM, Glenn Morris wrote:
> I really can't see how this is something that "People do [...] all the
> time, often unwittingly"

Yes, you're right, I was exaggerating -- it used to be more
common, but it's rarer nowadays.

Anyway, now that this patch is waiting until after the feature
freeze, it can accommodate some cleanup changes.  I've attached
the revised version.  It speeds up file-accessible-directory-p
by doing it with one system call rather than two, avoids the
unnecessary NILP check in file-writable-p that we discussed earlier,
fixes a bug where file-writable-p thinks that one can create a file
in a directory even when one cannot, does a better job of checking
whether directories are searchable rather than merely whether they
exist, and closes a couple more races related to permissions checking.
None of this is urgent but I figured I'd write it up while I was
thinking about it.

This patch is relative to trunk bzr 110616.

euidaccess.txt
Description: Text document