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Re: [Nano-devel] [PATCH] pull in the futimens module from gnulib

From: Benno Schulenberg
Subject: Re: [Nano-devel] [PATCH] pull in the futimens module from gnulib
Date: Mon, 03 Apr 2017 19:56:52 +0200

On Mon, Apr 3, 2017, at 08:29, Kamil Dudka wrote:
> On Sunday, April 02, 2017 18:01:47 Benno Schulenberg wrote:
> > How exactly does the use of futimens prevent a symlink attack?
> It changes timestamps on the file descriptor, instead of the file name.

Okay, so the real change is: to operate on a file descriptor instead of
on a filename -- something that only futimens() provides, not utime().

> So, 
> if the attacker unlinks the backup file and creates a symlink with the same 
> file name (while the file descriptor is opened), futimens() will still change 
> timestamps on the backup file.  Otherwise, utime() would change timestamps
> on the attacker-provided symlink's target.

I don't see how changing a timestamp on an arbitrary file could
become dangerous, but... okay, it should not be allowed.


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