ar: Disallow directory traversal

[emaste]

Summary

Set ARCHIVE_EXTRACT_SECURE_SYMLINKS and ARCHIVE_EXTRACT_SECURE_NODOTDOT as in bsdtar to prevent extraction of archive entries whose pathnames contain .. or whose target directory would be altered by a symlink. Also disallow absolute pathnames.

We don't currently provide an option to disable this behaviour (as bsdtar's -P does). It is unlikely to be a problem in practice for ar(1), but the -P option is available if we want to allow it.

Reported by: Alexander Cherepanov <[e-mail]>
Elftoolchain ticket: 474

Test Plan

From https://sourceforge.net/p/elftoolchain/tickets/474/

~~~
printf '!<arch>\n%-48s%-10s`\n%-48s%-10s`\n' /tmp/file 0 ../file 0 > test.a
n% ./ar -xv test.a
x - /tmp/file
ar: warning: Absolute path '/tmp/file'
x - ../file
ar: warning: Path contains '..'
~~~

[emaste]

Author: emaste
Date: Thu Apr 9 13:45:17 2015
New Revision: 281311
URL: https://svnweb.freebsd.org/changeset/base/281311