[PATCH 3.19.y-ckt 064/130] sched: cls_flow: fix panic on filter replace

From: Kamal Mostafa
Date: Thu Aug 27 2015 - 18:34:37 EST

3.19.8-ckt6 -stable review patch. If anyone has any objections, please let me know.


From: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

commit 32b2f4b196b37695fdb42b31afcbc15399d6ef91 upstream.

The following test case causes a NULL pointer dereference in cls_flow:

tc filter add dev foo parent 1: handle 0x1 flow hash keys dst action ok
tc filter replace dev foo parent 1: pref 49152 handle 0x1 \
flow hash keys mark action drop

To be more precise, actually two different panics are fixed, the first
occurs because tcf_exts_init() is not called on the newly allocated
filter when we do a replace. And the second panic uncovered after that
happens since the arguments of list_replace_rcu() are swapped, the old
element needs to be the first argument and the new element the second.

Fixes: 70da9f0bf999 ("net: sched: cls_flow use RCU")
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: John Fastabend <john.r.fastabend@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
net/sched/cls_flow.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/sched/cls_flow.c b/net/sched/cls_flow.c
index 15d68f2..bca348a 100644
--- a/net/sched/cls_flow.c
+++ b/net/sched/cls_flow.c
@@ -419,6 +419,8 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
if (!fnew)
goto err2;

+ tcf_exts_init(&fnew->exts, TCA_FLOW_ACT, TCA_FLOW_POLICE);
fold = (struct flow_filter *)*arg;
if (fold) {
err = -EINVAL;
@@ -480,7 +482,6 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
fnew->mask = ~0U;
fnew->tp = tp;
get_random_bytes(&fnew->hashrnd, 4);
- tcf_exts_init(&fnew->exts, TCA_FLOW_ACT, TCA_FLOW_POLICE);

fnew->perturb_timer.function = flow_perturbation;
@@ -520,7 +521,7 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
if (*arg == 0)
list_add_tail_rcu(&fnew->list, &head->filters);
- list_replace_rcu(&fnew->list, &fold->list);
+ list_replace_rcu(&fold->list, &fnew->list);

*arg = (unsigned long)fnew;


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