On Saturday 2012-09-22 00:26, Jim Robinson wrote:
>
>The bug is that under reproducible conditions, it is possible for
>limit_mt_check() to execute and kmalloc() a structure which does not
>get initialized. Specifically, if 'r->cost' is non-zero, 'priv' is
>kmalloc()ed but not initialized. The result of this is that
>'priv->prev' and 'priv->credit' have bad values in them
>
>--8<-- (Jim's patch)
Without this patch the allocated 'priv' structure could be used without initializing. This
was causing premature rate-limit matches (i.e. limit_mt() returning 'true' when it shouldn't
have). This patch is a best guess as to how to initialize 'priv', and seems to work.
diff -Nur linux-2.6.32.8/net/netfilter/xt_limit.c.ORIG linux-2.6.32.8/net/netfilter/xt_limit.c
--- linux-2.6.32.8/net/netfilter/xt_limit.c.ORIG 2012-09-12 17:14:19.758371942 -0700
+++ linux-2.6.32.8/net/netfilter/xt_limit.c 2012-09-19 12:09:00.238416282 -0700
@@ -114,6 +114,32 @@
if (priv == NULL)
return false;
+ // Start of Infoblox patch.
+ // Zero out 'priv' for good measure.
+ memset(priv, 0, sizeof(*priv));
+ // This seems to fix the problem of priv not being initialized when
+ // r->cost is non-zero.
+ if (r->cost != 0) {
+ // Note that non-zero r->cost seems to imply non-null
+ // r->master, however, better safe than sorry, so check r->master.
+ if (r->master != NULL) {
+ spin_lock_bh(&limit_lock);
+ priv->prev = r->master->prev;
+ priv->credit = r->master->credit;
+ spin_unlock_bh(&limit_lock);
+ } else {
+ // Not sure if this can ever happen. And definitely not sure
+ // if this is the right thing to do, however, priv needs to be
+ // initialized to something.
+ printk("limit_mt_check: unexpected non-zero cost and null master\n");
+ priv->prev = jiffies;
+ priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
+ }
+ r->master = priv;
+ return true;
+ }
+ // End of Infoblox patch.
+
/* For SMP, we only want to use one set of state. */
r->master = priv;
if (r->cost == 0) {
--
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