netdev - [PATCH net 3/3] sched: cls_flow: fix panic on filter replace

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Message-Id: <e9ed6bbcf7e9d9b3fdbd3dd0b5117d9a284b4399.1437163466.git.daniel@iogearbox.net>
Date:	Fri, 17 Jul 2015 22:38:45 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	davem@...emloft.net
Cc:	ast@...mgrid.com, jiri@...nulli.us, jhs@...atatu.com,
	edumazet@...gle.com, netdev@...r.kernel.org,
	Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH net 3/3] sched: cls_flow: fix panic on filter replace

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@...earbox.net>
---
 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 76bc3a2..bb2a0f5 100644
--- a/net/sched/cls_flow.c
+++ b/net/sched/cls_flow.c
@@ -425,6 +425,8 @@ 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;
@@ -486,7 +488,6 @@ 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;
@@ -526,7 +527,7 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
 	if (*arg == 0)
 		list_add_tail_rcu(&fnew->list, &head->filters);
 	else
-		list_replace_rcu(&fnew->list, &fold->list);
+		list_replace_rcu(&fold->list, &fnew->list);
 
 	*arg = (unsigned long)fnew;
 
-- 
1.9.3

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