The returned value from snprintf() should be checked carefully.

This bug can be leveraged to execute arbitrary code through carefully
constructing the payload, e.g,

lxc-freeze -n `python -c "print 'AAAAAAAA' + 'B'*959"` -P PADPAD -o /tmp/log

This command running on Ubuntu 14.04 (x86-64) can cause a segment fault.
Signed-off-by: Lans Zhang <jia.zhang@windriver.com>