[PATCH v4 2/5] fs: Add fchmodat2()

David Laight David.Laight at ACULAB.COM
Fri Jul 28 18:43:58 AEST 2023

> FWIW, I agree with Christian that these behaviours are not ideal (and
> I'm working on a series that might allow for these things to be properly
> blocked in the future) but there's also the consistency argument -- I
> don't think fchownat() is much safer to allow in this way than
> fchmodat() and (again) this behaviour is already possible through
> procfs.

If the 'through procfs' involves readlink("/proc/self/fd/n") and
accessing through the returned path then the permission checks
are different.
Using the returned path requires search permissions on all the

This is all fine for xxxat() functions where a real open
directory fd is supplied.
But other cases definitely need a lot of thought to ensure
they don't let programs acquire permissions they aren't
supposed to have.


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