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Fix slab corruption with netem (2nd try)

PATCH In review Guillaume Chazarain 2 participants 2 messages Jul 16, 2006 – Jul 17, 2006

Subsystems (4)
Networking Network drivers Traffic control (tc) Netem network emulator
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Guillaume Chazarain

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#0 lore raw

PATCH 1/1 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]

Thanks.

Signature · 1 line
Guillaume
Signed-off-by Guillaume Chazarain <[email protected]>
---
 net/sched/sch_netem.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
net/sched/sch_netem.c +3 -1
diff -r 1b8d63e34819 net/sched/sch_netem.c
@@ -148,7 +148,8 @@ static int netem_enqueue(struct sk_buff 
 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->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)) {
maintainer
#1 lore raw

From: Guillaume Chazarain <[email protected]>
Date: Sun, 16 Jul 2006 23:56:31 +0200

Quoted 11 lines

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]

Looks good to me, applied, thanks a lot.