I might be wrong, but can't you use udev rules, to assign 0666 permissions when /dev/knem is mounted ?
Controlling permissions and ownership
udev allows you to use additional assignments in rules to control ownership and permission attributes on each device.
The GROUP assignment allows you to define which Unix group should own the device node. Here is an example rule which defines that the video group will own the framebuffer devices:
KERNEL=="fb[0-9]*", NAME="fb/%n", SYMLINK+="%k", GROUP="video"
The OWNER key, perhaps less useful, allows you to define which Unix user should have ownership permissions on the device node. Assuming the slightly odd situation where you would want john to own your floppy devices, you could use:
udev defaults to creating nodes with Unix permissions of 0660 (read/write to owner and group). If you need to, you can override these defaults on certain devices using rules including the MODE assignment. As an example, the following rule defines that the inotify node shall be readable and writable to everyone:
KERNEL=="inotify", NAME="misc/%k", SYMLINK+="%k", MODE="0666"
A step-by-step on creting UDEV rules can be found in this post: http://ubuntuforums.org/showthread.php?t=168221