Commit 89e1df74 authored Jul 21, 2006 by Guillaume Chazarain Committed by David S. Miller Jul 21, 2006

[PKT_SCHED] netem: Fix slab corruption with netem (2nd try)



CONFIG_DEBUG_SLAB found the following bug:
netem_enqueue() in sch_netem.c gets a pointer inside a slab object:
struct netem_skb_cb *cb = (struct netem_skb_cb *)skb->cb;
But then, the slab object may be freed:
skb = skb_unshare(skb, GFP_ATOMIC)
cb is still pointing inside the freed skb, so here is a patch to
initialize cb later, and make it clear that initializing it sooner
is a bad idea.

[From Stephen Hemminger: leave cb unitialized in order to let gcc
complain in case of use before initialization]

Signed-off-by: Guillaume Chazarain <guichaz@yahoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent fbeff3c1

net/sched/sch_netem.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -148,7 +148,8 @@ static long tabledist(unsigned long mu, long sigma,
		static int netem_enqueue(struct sk_buff skb, struct Qdisc sch)
		{
		struct netem_sched_data *q = qdisc_priv(sch);
		struct netem_skb_cb cb = (struct netem_skb_cb )skb->cb;
		/* We don't fill cb now as skb_unshare() may invalidate it */
		struct netem_skb_cb *cb;
		struct sk_buff *skb2;
		int ret;
		int count = 1;
		@@ -200,6 +201,7 @@ static int netem_enqueue(struct sk_buff skb, struct Qdisc sch)
		skb->data[net_random() % skb_headlen(skb)] ^= 1<<(net_random() % 8);
		}

		cb = (struct netem_skb_cb *)skb->cb;
		if (q->gap == 0 /* not doing reordering */
		\|\| q->counter < q->gap /* inside last reordering gap */
		\|\| q->reorder < get_crandom(&q->reorder_cor)) {

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