+/**
+ * xt_check_entry_offsets - validate arp/ip/ip6t_entry
+ *
+ * @base: pointer to arp/ip/ip6t_entry
+ * @elems: pointer to first xt_entry_match, i.e. ip(6)t_entry->elems
+ * @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 and that all
+ * match sizes (if any) align with the target offset.
+ *
+ * This function does not validate the targets or matches themselves, it
+ * only tests that all the offsets and sizes are correct, that all
+ * match structures are aligned, and that the last structure ends where
+ * the target structure begins.
+ *
+ * Also see xt_compat_check_entry_offsets for CONFIG_COMPAT version.
+ *
+ * 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.
+ *
+ * A well-formed entry looks like this:
+ *
+ * ip(6)t_entry match [mtdata] match [mtdata] target [tgdata] ip(6)t_entry
+ * e->elems[]-----' | |
+ * matchsize | |
+ * matchsize | |
+ * | |
+ * target_offset---------------------------------' |
+ * next_offset---------------------------------------------------'
+ *
+ * elems[]: flexible array member at end of ip(6)/arpt_entry struct.
+ * This is where matches (if any) and the target reside.
+ * target_offset: beginning of target.
+ * next_offset: start of the next rule; also: size of this rule.
+ * Since targets have a minimum size, target_offset + minlen <= next_offset.
+ *
+ * Every match stores its size, sum of sizes must not exceed target_offset.
+ *
+ * Return: 0 on success, negative errno on failure.
+ */
+int xt_check_entry_offsets(const void *base,
+ const char *elems,
+ unsigned int target_offset,
+ unsigned int next_offset)
+{
+ long size_of_base_struct = elems - (const char *)base;
+ const struct xt_entry_target *t;
+ const char *e = base;
+
+ /* target start is within the ip/ip6/arpt_entry struct */
+ if (target_offset < size_of_base_struct)
+ return -EINVAL;
+
+ if (target_offset + sizeof(*t) > next_offset)
+ return -EINVAL;
+
+ t = (void *)(e + target_offset);
+ if (t->u.target_size < sizeof(*t))
+ return -EINVAL;
+
+ if (target_offset + t->u.target_size > next_offset)
+ return -EINVAL;
+
+ if (strcmp(t->u.user.name, XT_STANDARD_TARGET) == 0 &&
+ XT_ALIGN(target_offset + sizeof(struct xt_standard_target)) != next_offset)
+ return -EINVAL;
+
+ return xt_check_entry_match(elems, base + target_offset,
+ __alignof__(struct xt_entry_match));
+}
+EXPORT_SYMBOL(xt_check_entry_offsets);
+