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

[David Laight <David.Laight@xxxxxxxxxx>]

From: Aleksa Sarai
> Sent: 25 July 2023 17:36
...
> We almost certainly want to support AT_EMPTY_PATH at the same time.
> Otherwise userspace will still need to go through /proc when trying to
> chmod a file handle they have.

That can't be allowed.

Just because a process has a file open and write access to
the directory that contains it doesn't mean they are allowed
to change the file permissions.

They also need directory search access from a directory
they have open through to the containing directory.

	David

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