[EBTABLES]: Prevent wraparounds in checks for entry components' sizes.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/netfilter/ebtables.c

@@ -338,10 +338,11 @@ ebt_check_match(struct ebt_entry_match *m, struct ebt_entry *e,
    const char *name, unsigned int hookmask, unsigned int *cnt)
 {
 	struct ebt_match *match;
+	size_t left = ((char *)e + e->watchers_offset) - (char *)m;
 	int ret;
 
-	if (((char *)m) + m->match_size + sizeof(struct ebt_entry_match) >
-	   ((char *)e) + e->watchers_offset)
+	if (left < sizeof(struct ebt_entry_match) ||
+	    left - sizeof(struct ebt_entry_match) < m->match_size)
 		return -EINVAL;
 	match = find_match_lock(m->u.name, &ret, &ebt_mutex);
 	if (!match)
@@ -367,10 +368,11 @@ ebt_check_watcher(struct ebt_entry_watcher *w, struct ebt_entry *e,
    const char *name, unsigned int hookmask, unsigned int *cnt)
 {
 	struct ebt_watcher *watcher;
+	size_t left = ((char *)e + e->target_offset) - (char *)w;
 	int ret;
 
-	if (((char *)w) + w->watcher_size + sizeof(struct ebt_entry_watcher) >
-	   ((char *)e) + e->target_offset)
+	if (left < sizeof(struct ebt_entry_watcher) ||
+	   left - sizeof(struct ebt_entry_watcher) < w->watcher_size)
 		return -EINVAL;
 	watcher = find_watcher_lock(w->u.name, &ret, &ebt_mutex);
 	if (!watcher)
@@ -573,6 +575,7 @@ ebt_check_entry(struct ebt_entry *e, struct ebt_table_info *newinfo,
 	struct ebt_entry_target *t;
 	struct ebt_target *target;
 	unsigned int i, j, hook = 0, hookmask = 0;
+	size_t gap = e->next_offset - e->target_offset;
 	int ret;
 
 	/* don't mess with the struct ebt_entries */
@@ -634,8 +637,7 @@ ebt_check_entry(struct ebt_entry *e, struct ebt_table_info *newinfo,
 
 	t->u.target = target;
 	if (t->u.target == &ebt_standard_target) {
-		if (e->target_offset + sizeof(struct ebt_standard_target) >
-		   e->next_offset) {
+		if (gap < sizeof(struct ebt_standard_target)) {
 			BUGPRINT("Standard target size too big\n");
 			ret = -EFAULT;
 			goto cleanup_watchers;
@@ -646,8 +648,7 @@ ebt_check_entry(struct ebt_entry *e, struct ebt_table_info *newinfo,
 			ret = -EFAULT;
 			goto cleanup_watchers;
 		}
-	} else if ((e->target_offset + t->target_size +
-	   sizeof(struct ebt_entry_target) > e->next_offset) ||
+	} else if (t->target_size > gap - sizeof(struct ebt_entry_target) ||
 	   (t->u.target->check &&
 	   t->u.target->check(name, hookmask, e, t->data, t->target_size) != 0)){
 		module_put(t->u.target->me);