This trick is for multiuser boxes to try and ammeleriate issues with people creating insecure temporary files (and to make it obvious which applications don't respect TMPDIR). The idea is to create a seperate directory for every user on the machine that's 700 to that user and point TMPDIR at it. I think that this idea could(/should?) be used by default by distributions. This can be extended to work for other services (eg apache).
Points for:
mkdir -p /tmp/$USER/create.$$ 2>/dev/null if [ -O /tmp/$USER?; then
TMPDIR=/tmp/$USER
else
TMPDIR=$(mktemp -d /tmp/${USER}.XXXXXX)
fi
touch $TMPDIR/.bash.$$ [ -d $TMPDIR/create.$$? && rmdir $TMPDIR/create.$$
TMP=$TMPDIR TEMP=$TMPDIR
export TMPDIR TMP TEMP
This means that it will remove the directory when the last shell is closed and there are no more files in the directory.
The reason for creating then deleting $TMPDIR/create.$$, as some may wonder, is to make the mkdir an atomic operation that should stop any shell that is logging out as you log in, from removing $TMPDIR before a file is created within it ($TMPDIR/.bash.$$)
If users want scratch space to copy files between users etc, they can use /tmp directly as LFS suggests, however conformant programs should use TMPDIR which now places the files in /tmp/username or /tmp/username.uniqueid.
The current flaw with this script is that it doesn't detect if /tmp/username and all the possible /tmp/username.uniqueids have already been created by an attacker.
Alternatively the first script can be placed in /etc/profile.d/ and the .bash_logout script can be ignored and the directories can be removed regularly from cron if necessary.
Ideally Linux could transparently produce a unique /tmp/ for each $USER on the system, but that would break LinuxStandardsBase compiliance and many applications.
One page links to PerUserTempDirs: