[PATCH 4.14 38/40] net: sched: act_sample: fix psample group handling on overwrite

Greg Kroah-Hartman
2019-09-08T12:46:35Z

From: Vlad Buslov <vladbu@mellanox.com>

[ Upstream commit dbf47a2a094edf58983265e323ca4bdcdb58b5ee ]

Action sample doesn't properly handle psample_group pointer in overwrite
case. Following issues need to be fixed:

- In tcf_sample_init() function RCU_INIT_POINTER() is used to set
s->psample_group, even though we neither setting the pointer to NULL, nor
preventing concurrent readers from accessing the pointer in some way.
Use rcu_swap_protected() instead to safely reset the pointer.

- Old value of s->psample_group is not released or deallocated in any way,
which results resource leak. Use psample_group_put() on non-NULL value
obtained with rcu_swap_protected().

- The function psample_group_put() that released reference to struct
psample_group pointed by rcu-pointer s->psample_group doesn't respect rcu
grace period when deallocating it. Extend struct psample_group with rcu
head and use kfree_rcu when freeing it.

Fixes: 5c5670fae430 ("net/sched: Introduce sample tc action")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/psample.h | 1 +
net/psample/psample.c | 2 +-
net/sched/act_sample.c | 5 ++++-
3 files changed, 6 insertions(+), 2 deletions(-)

--- a/include/net/psample.h
+++ b/include/net/psample.h
@@ -12,6 +12,7 @@ struct psample_group {
u32 group_num;
u32 refcount;
u32 seq;
+ struct rcu_head rcu;
};

struct psample_group *psample_group_get(struct net *net, u32 group_num);
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -156,7 +156,7 @@ static void psample_group_destroy(struct
{
psample_group_notify(group, PSAMPLE_CMD_DEL_GROUP);
list_del(&group->list);
- kfree(group);
+ kfree_rcu(group, rcu);
}

static struct psample_group *
--- a/net/sched/act_sample.c
+++ b/net/sched/act_sample.c
@@ -92,13 +92,16 @@ static int tcf_sample_init(struct net *n
tcf_idr_release(*a, bind);
return -ENOMEM;
}
- RCU_INIT_POINTER(s->psample_group, psample_group);
+ rcu_swap_protected(s->psample_group, psample_group,
+ lockdep_is_held(&s->tcf_lock));

if (tb[TCA_SAMPLE_TRUNC_SIZE]) {
s->truncate = true;
s->trunc_size = nla_get_u32(tb[TCA_SAMPLE_TRUNC_SIZE]);
}

+ if (psample_group)
+ psample_group_put(psample_group);
if (ret == ACT_P_CREATED)
tcf_idr_insert(tn, *a);
return ret;