[patch] ebtables: don't compute gap before checking struct type

[Chuck Ebbert <76306.1226@compuserve.com>]

We cannot compute the gap until we know we have a 'struct ebt_entry'
and not 'struct ebt_entries'.  Failure to check can cause crash.

Tested by Santiago Garcia Mantinan <manty@manty.net>

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
---
Can we get this upstream quickly?  The bug's also in 2.6.19.1 and
2.6.18.6.

--- 2.6.20-rc1-32smp.orig/net/bridge/netfilter/ebtables.c
+++ 2.6.20-rc1-32smp/net/bridge/netfilter/ebtables.c
@@ -610,7 +610,7 @@ ebt_check_entry(struct ebt_entry *e, str
 	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;
+	size_t gap;
 	int ret;
 
 	/* don't mess with the struct ebt_entries */
@@ -660,6 +660,7 @@ ebt_check_entry(struct ebt_entry *e, str
 	if (ret != 0)
 		goto cleanup_watchers;
 	t = (struct ebt_entry_target *)(((char *)e) + e->target_offset);
+	gap = e->next_offset - e->target_offset;
 	target = find_target_lock(t->u.name, &ret, &ebt_mutex);
 	if (!target)
 		goto cleanup_watchers;
-- 
MBTI: IXTP