netfilter: x_tables: add and use xt_check_entry_offsets

[karo-tx-linux.git] / net / netfilter / x_tables.c

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index d4aaad747ea99b0aa877016f437a5fd46ec768ee..24a9dfb51df23ea2369096ade7d216a1bf046e26 100644 (file)
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -540,6 +540,40 @@ int xt_compat_match_to_user(const struct xt_entry_match *m,
 EXPORT_SYMBOL_GPL(xt_compat_match_to_user);
 #endif /* CONFIG_COMPAT */
 
+/**
+ * xt_check_entry_offsets - validate arp/ip/ip6t_entry
+ *
+ * @base: pointer to arp/ip/ip6t_entry
+ * @target_offset: the arp/ip/ip6_t->target_offset
+ * @next_offset: the arp/ip/ip6_t->next_offset
+ *
+ * validates that target_offset and next_offset are sane.
+ *
+ * The arp/ip/ip6t_entry structure @base must have passed following tests:
+ * - it must point to a valid memory location
+ * - base to base + next_offset must be accessible, i.e. not exceed allocated
+ *   length.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int xt_check_entry_offsets(const void *base,
+                          unsigned int target_offset,
+                          unsigned int next_offset)
+{
+       const struct xt_entry_target *t;
+       const char *e = base;
+
+       if (target_offset + sizeof(*t) > next_offset)
+               return -EINVAL;
+
+       t = (void *)(e + target_offset);
+       if (target_offset + t->u.target_size > next_offset)
+               return -EINVAL;
+
+       return 0;
+}
+EXPORT_SYMBOL(xt_check_entry_offsets);
+
 int xt_check_target(struct xt_tgchk_param *par,
                    unsigned int size, u_int8_t proto, bool inv_proto)
 {