[PATCH] audit: fix broken class-based syscall audit

[Klaus Weidner <klaus@atsec.com>]

Bug description: When I add an audit watch on a file with no arguments, I
get perm=rwxa but on ia64, changes to the mode and context aren't
audited.  I get audit records on i386 and x86_64.
(from https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=239887 )

The sanity check in audit_match_class() is wrong, AUDIT_BITMASK_SIZE is
64, providing space for 2048 syscalls in 64 * 32bit integers. The
comparison only supports 256 syscalls (sizeof __u32 is 4), and silently
returns "no match" for valid higher-numbered syscalls.

This breaks class-based audit for all syscalls on ia64 since on that
architecture syscall numbers start at 1024. It breaks some syscall audit
on other architectures also, for example __NR_fchmodat is 306 on x86.

I'd suggest adding a printk() in addition to returning 0 - you don't want
to silently ignore unknown or unsupported syscalls when auditing.

Signed-off-by: Klaus Weidner <klaus@atsec.com>

Followup discussion was on the linux-audit mailing list:

 https://www.redhat.com/archives/linux-audit/2007-May/msg00030.html

Acked-by: Al Viro <viro@zeniv.linux.org.uk>

--- linux-2.6.18.i686/kernel/auditfilter.c.lspp.80	2007-05-11 17:06:08.000000000 -0500
+++ linux-2.6.18.i686/kernel/auditfilter.c	2007-05-11 17:09:37.000000000 -0500
@@ -306,7 +306,7 @@
 
 int audit_match_class(int class, unsigned syscall)
 {
-	if (unlikely(syscall >= AUDIT_BITMASK_SIZE * sizeof(__u32)))
+	if (unlikely(syscall >= AUDIT_BITMASK_SIZE * 32))
 		return 0;
 	if (unlikely(class >= AUDIT_SYSCALL_CLASSES || !classes[class]))
 		return 0;