bug#6925: strange behavior of mktemp (GNU coreutils) 7.4, Ubuntu 10.04)

[Eric Blake]

On 08/27/2010 07:08 AM, master atomknuseren wrote:
> When I invoke mktemp in a script as:
>
> #!/bin/bash
> DIR=$( mktemp||exit 1 )
> cd $DIR
> echo $?
>
> I receive an error like:
> --
> can't cd to /tmp/tmp.68rHO2a3jc

Thanks for the report.  However, this is not a bug.

If you want mktemp to create a directory instead of a file, you must use 
the -d option.  As written, you created a file, which means of course cd 
will fail because it is not a directory.

> My primitive workaround is to recreate  $DIR as in:
> #!/bin/bash
> DIR=$( mktemp||exit 1 )
> rm -r -f $DIR
> mkdir -p $DIR

Heavens no.  This introduces a data race that exposes you to the very 
bug that you are trying to avoid by using mktemp in the first place - 
namely, a window where an attacker can spot the filename you are using 
and inject a rogue file in it's place in the time where the file does 
not exist.

Rather, by using DIR=$(mktemp -d), you are guaranteed to have a 
directory or a failure, without having to call mkdir -p after the fact.

By the way, the ||exit 1 in your command substitution is pointless.

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org