GNU bug report logs - #12366
[gnu-prog-discuss] Writing unwritable files

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Paolo Bonzini <bonzini <at> gnu.org>
Cc: 12366 <at> debbugs.gnu.org, gnu-prog-discuss <at> gnu.org, John Darrington <john <at> darrington.wattle.id.au>
Subject: bug#12366: [gnu-prog-discuss] Writing unwritable files
Date: Thu, 06 Sep 2012 09:11:52 -0700

On 09/06/2012 05:12 AM, Paolo Bonzini wrote:
> I consider "shuf foo -o foo" (on a read-write file) to be insecure.
> Besides, it works by chance

It's not by chance.  shuf is designed to let you
shuffle a file in-place, and is documented to work,
by analogy with "sort -o foo foo".  If we ever
change "shuf" to use mmap, we'll make
sure it continues to work in-place.

I'm not sure what is meant by "insecure" here.
Of course there are race conditions if other
processes modify a file when "shuf"
reads or writes it, but that's true for pretty
much any program that reads or writes any file,
including sed -i.

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