tree 39ca4e05c0dda995f3eaaea1aaa2c8689003f1d0
parent 5801649d8b83e7cb9b15839761bdee594653c294
author Michael LeMay <mdlemay@epoch.ncsc.mil> 1151306694 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> 1151341098 -0700

[PATCH] keys: allocate key serial numbers randomly

Cause key_alloc_serial() to generate key serial numbers randomly rather than
in linear sequence.

Using an linear sequence permits a covert communication channel to be
established, in which one process can communicate with another by creating or
not creating new keys within a certain timeframe.  The second process can
probe for the expected next key serial number and judge its existence by the
error returned.

This is a problem as the serial number namespace is globally shared between
all tasks, regardless of their context.

For more information on this topic, this old TCSEC guide is recommended:

	http://www.radium.ncsc.mil/tpep/library/rainbow/NCSC-TG-030.html

Signed-off-by: Michael LeMay <mdlemay@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@namei.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>