sys_prctl(): arg2 is unsigned long which is never < 0

arg2 will never < 0, for its type is 'unsigned long'

Also, use the provided macros.
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Reported-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys.c

@@ -47,6 +47,7 @@
 #include <linux/syscalls.h>
 #include <linux/kprobes.h>
 #include <linux/user_namespace.h>
+#include <linux/binfmts.h>
 
 #include <linux/kmsg_dump.h>
 /* Move somewhere else to avoid recompiling? */
@@ -2026,7 +2027,8 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			error = get_dumpable(me->mm);
 			break;
 		case PR_SET_DUMPABLE:
-			if (arg2 < 0 || arg2 > 1) {
+			if (arg2 != SUID_DUMP_DISABLE &&
+			    arg2 != SUID_DUMP_USER) {
 				error = -EINVAL;
 				break;
 			}