[PATCH] Filter rule comparators

Currently, audit only supports the "=" and "!=" operators in the -F
filter rules.

This patch reworks the support for "=" and "!=", and adds support
for ">", ">=", "<", and "<=".

This turned out to be a pretty clean, and simply process.  I ended up
using the high order bits of the "field", as suggested by Steve and Amy.
This allowed for no changes whatsoever to the netlink communications.
See the documentation within the patch in the include/linux/audit.h
area, where there is a table that explains the reasoning of the bitmask
assignments clearly.

The patch adds a new function, audit_comparator(left, op, right).
This function will perform the specified comparison (op, which defaults
to "==" for backward compatibility) between two values (left and right).
If the negate bit is on, it will negate whatever that result was.  This
value is returned.

Signed-off-by: Dustin Kirkland <dustin.kirkland@us.ibm.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

1 files changed, 28 insertions, 1 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index da3c01955f3d..2408cb77899c 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -98,6 +98,13 @@
 #define AUDIT_WORD(nr) ((__u32)((nr)/32))
 #define AUDIT_BIT(nr)  (1 << ((nr) - AUDIT_WORD(nr)*32))
 
+/* This bitmask is used to validate user input.  It represents all bits that
+ * are currently used in an audit field constant understood by the kernel.
+ * If you are adding a new #define AUDIT_<whatever>, please ensure that
+ * AUDIT_UNUSED_BITS is updated if need be. */
+#define AUDIT_UNUSED_BITS       0x0FFFFC00
+
+
 /* Rule fields */
                                 /* These are useful when checking the
                                  * task structure at task creation time
@@ -128,8 +135,28 @@
 #define AUDIT_ARG2      (AUDIT_ARG0+2)
 #define AUDIT_ARG3      (AUDIT_ARG0+3)
 
-#define AUDIT_NEGATE    0x80000000
+#define AUDIT_NEGATE                    0x80000000
 
+/* These are the supported operators.
+ *      4  2  1
+ *      =  >  <
+ *      -------
+ *      0  0  0         0       nonsense
+ *      0  0  1         1       <
+ *      0  1  0         2       >
+ *      0  1  1         3       !=
+ *      1  0  0         4       =
+ *      1  0  1         5       <=
+ *      1  1  0         6       >=
+ *      1  1  1         7       all operators
+ */
+#define AUDIT_LESS_THAN                 0x10000000
+#define AUDIT_GREATER_THAN              0x20000000
+#define AUDIT_NOT_EQUAL                 0x30000000
+#define AUDIT_EQUAL                     0x40000000
+#define AUDIT_LESS_THAN_OR_EQUAL        (AUDIT_LESS_THAN|AUDIT_EQUAL)
+#define AUDIT_GREATER_THAN_OR_EQUAL     (AUDIT_GREATER_THAN|AUDIT_EQUAL)
+#define AUDIT_OPERATORS                 (AUDIT_EQUAL|AUDIT_NOT_EQUAL)
 
 /* Status symbols */
                                 /* Mask values */