[PATCH] remove untrusted chars read from sysfs-values or returned by PROGRAM

[PATCH] remove untrusted chars read from sysfs-values or returned by PROGRAM

Better remove characters that are useless in a device node name.
It may be a security risk to pass any character read from e.g. a
sysfs attribute to a shell script we execute later.

Prevent the modification of the libsysfs attribute value
cache.

Clear PROGRAM result if the execution encountered an error.