>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) {
r->master does not have any sensical value when it's coming from userspace.
>+ 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) {
A patch I think is better comes as reply to this message.
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