+/* Standard flags in GUE header */
+
+#define GUE_FLAG_PRIV htons(1<<0) /* Private flags are in options */
+#define GUE_LEN_PRIV 4
+
+#define GUE_FLAGS_ALL (GUE_FLAG_PRIV)
+
+/* Private flags in the private option extension */
+
+#define GUE_PFLAG_REMCSUM htonl(1 << 31)
+#define GUE_PLEN_REMCSUM 4
+
+#define GUE_PFLAGS_ALL (GUE_PFLAG_REMCSUM)
+
+/* Functions to compute options length corresponding to flags.
+ * If we ever have a lot of flags this can be potentially be
+ * converted to a more optimized algorithm (table lookup
+ * for instance).
+ */
+static inline size_t guehdr_flags_len(__be16 flags)
+{
+ return ((flags & GUE_FLAG_PRIV) ? GUE_LEN_PRIV : 0);
+}
+
+static inline size_t guehdr_priv_flags_len(__be32 flags)
+{
+ return 0;
+}
+
+/* Validate standard and private flags. Returns non-zero (meaning invalid)
+ * if there is an unknown standard or private flags, or the options length for
+ * the flags exceeds the options length specific in hlen of the GUE header.
+ */
+static inline int validate_gue_flags(struct guehdr *guehdr,
+ size_t optlen)
+{
+ size_t len;
+ __be32 flags = guehdr->flags;
+
+ if (flags & ~GUE_FLAGS_ALL)
+ return 1;
+
+ len = guehdr_flags_len(flags);
+ if (len > optlen)
+ return 1;
+
+ if (flags & GUE_FLAG_PRIV) {
+ /* Private flags are last four bytes accounted in
+ * guehdr_flags_len
+ */
+ flags = *(__be32 *)((void *)&guehdr[1] + len - GUE_LEN_PRIV);
+
+ if (flags & ~GUE_PFLAGS_ALL)
+ return 1;
+
+ len += guehdr_priv_flags_len(flags);
+ if (len > optlen)
+ return 1;
+ }
+
+ return 0;
+}
+