[PATCH 4.1 138/159] sched: cls_flow: fix panic on filter replace

Greg Kroah-Hartman
2015-09-26T21:18:20Z

From: Daniel Borkmann <daniel@iogearbox.net>

[ Upstream commit 32b2f4b196b37695fdb42b31afcbc15399d6ef91 ]

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@iogearbox.net>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_flow.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/sched/cls_flow.c
+++ b/net/sched/cls_flow.c
@@ -419,6 +419,8 @@ static int flow_change(struct net *net,
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,
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,
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;