netfilter: xt_recent: check for unsupported user space flags

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/linux/netfilter/xt_recent.h

@@ -20,6 +20,9 @@ enum {
 /* Only allowed with --rcheck and --update */
 #define XT_RECENT_MODIFIERS (XT_RECENT_TTL|XT_RECENT_REAP)
 
+#define XT_RECENT_VALID_FLAGS (XT_RECENT_CHECK|XT_RECENT_SET|XT_RECENT_UPDATE|\
+			       XT_RECENT_REMOVE|XT_RECENT_TTL|XT_RECENT_REAP)
+
 struct xt_recent_mtinfo {
 	__u32 seconds;
 	__u32 hit_count;

net/netfilter/xt_recent.c

@@ -319,6 +319,11 @@ static bool recent_mt_check(const struct xt_mtchk_param *par)
 		get_random_bytes(&hash_rnd, sizeof(hash_rnd));
 		hash_rnd_inited = true;
 	}
+	if (info->check_set & ~XT_RECENT_VALID_FLAGS) {
+		pr_info(KBUILD_MODNAME ": Unsupported user space flags "
+			"(%08x)\n", info->check_set);
+		return false;
+	}
 	if (hweight8(info->check_set &
 		     (XT_RECENT_SET | XT_RECENT_REMOVE |
 		      XT_RECENT_CHECK | XT_RECENT_UPDATE)) != 1)