[PATCH] Fix audit operators

Darrel Goeddel initiated a discussion on IRC regarding the possibility
of audit_comparator() returning -EINVAL signaling an invalid operator.

It is possible when creating the rule to assure that the operator is one
of the 6 sane values.  Here's a snip from include/linux/audit.h  Note
that 0 (nonsense) and 7 (all operators) are not valid values for an
operator.

...

/* 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
 */
...

Furthermore, prior to adding these extended operators, flagging the
AUDIT_NEGATE bit implied !=, and otherwise == was assumed.

The following code forces the operator to be != if the AUDIT_NEGATE bit
was flipped on.  And if no operator was specified, == is assumed.  The
only invalid condition is if the AUDIT_NEGATE bit is off and all of the
AUDIT_EQUAL, AUDIT_LESS_THAN, and AUDIT_GREATER_THAN bits are
on--clearly a nonsensical operator.

Now that this is handled at rule insertion time, the default -EINVAL
return of audit_comparator() is eliminated such that the function can
only return 1 or 0.

If this is acceptable, let's get this applied to the current tree.

:-Dustin

--
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from 9bf0a8e137040f87d1b563336d4194e38fb2ba1a commit)

kernel/auditfilter.c

@@ -160,11 +160,17 @@ static struct audit_entry *audit_rule_to_entry(struct audit_rule *rule)
 		f->val = rule->values[i];
 
 		entry->rule.vers_ops = (f->op & AUDIT_OPERATORS) ? 2 : 1;
+
+		/* Support for legacy operators where
+		 * AUDIT_NEGATE bit signifies != and otherwise assumes == */
 		if (f->op & AUDIT_NEGATE)
-			f->op |= AUDIT_NOT_EQUAL;
-		else if (!(f->op & AUDIT_OPERATORS))
-			f->op |= AUDIT_EQUAL;
-		f->op &= ~AUDIT_NEGATE;
+			f->op = AUDIT_NOT_EQUAL;
+		else if (!f->op)
+			f->op = AUDIT_EQUAL;
+		else if (f->op == AUDIT_OPERATORS) {
+			err = -EINVAL;
+			goto exit_free;
+		}
 	}
 
 exit_nofree:
@@ -533,9 +539,9 @@ int audit_comparator(const u32 left, const u32 op, const u32 right)
 		return (left > right);
 	case AUDIT_GREATER_THAN_OR_EQUAL:
 		return (left >= right);
-	default:
-		return -EINVAL;
 	}
+	BUG();
+	return 0;
 }