audit: ignore terminating NUL in AUDIT_USER_TTY messages

audit: ignore terminating NUL in AUDIT_USER_TTY messages

AUDIT_USER_TTY, like all other messages sent from user-space, is sent
NUL-terminated.  Unlike other user-space audit messages, which come only
from trusted sources, AUDIT_USER_TTY messages are processed using
audit_log_n_untrustedstring().

This patch modifies AUDIT_USER_TTY handling to ignore the trailing NUL
and use the "quoted_string" representation of the message if possible.

Signed-off-by: Miloslav Trmac <[email protected]>
Cc: Eric Paris <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Steve Grubb <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>