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drop_monitor: Make updating data->skb smp safe

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Eric Dumazet pointed out to me that the drop_monitor protocol has some holes in
its smp protections.  Specifically, its possible to replace data->skb while its
being written.  This patch corrects that by making data->skb an rcu protected
variable.  That will prevent it from being overwritten while a tracepoint is
modifying it.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: David Miller <davem@davemloft.net>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neil Horman 2012-04-27 10:11:49 +00:00 committed by David S. Miller
parent cde2e9a651
commit 3885ca785a
1 changed files with 54 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
net/core/drop_monitor.c
View File

@ -46,7 +46,7 @@ static DEFINE_MUTEX(trace_state_mutex);
struct per_cpu_dm_data {
struct work_struct dm_alert_work;
struct sk_buff *skb;
struct sk_buff __rcu *skb;
atomic_t dm_hit_count;
struct timer_list send_timer;
};
@ -73,35 +73,58 @@ static int dm_hit_limit = 64;
static int dm_delay = 1;
static unsigned long dm_hw_check_delta = 2*HZ;
static LIST_HEAD(hw_stats_list);
static int initialized = 0;
static void reset_per_cpu_data(struct per_cpu_dm_data *data)
{
size_t al;
struct net_dm_alert_msg *msg;
struct nlattr *nla;
struct sk_buff *skb;
struct sk_buff *oskb = rcu_dereference_protected(data->skb, 1);
al = sizeof(struct net_dm_alert_msg);
al += dm_hit_limit * sizeof(struct net_dm_drop_point);
al += sizeof(struct nlattr);
data->skb = genlmsg_new(al, GFP_KERNEL);
genlmsg_put(data->skb, 0, 0, &net_drop_monitor_family,
0, NET_DM_CMD_ALERT);
nla = nla_reserve(data->skb, NLA_UNSPEC, sizeof(struct net_dm_alert_msg));
msg = nla_data(nla);
memset(msg, 0, al);
atomic_set(&data->dm_hit_count, dm_hit_limit);
skb = genlmsg_new(al, GFP_KERNEL);
if (skb) {
genlmsg_put(skb, 0, 0, &net_drop_monitor_family,
0, NET_DM_CMD_ALERT);
nla = nla_reserve(skb, NLA_UNSPEC,
sizeof(struct net_dm_alert_msg));
msg = nla_data(nla);
memset(msg, 0, al);
} else if (initialized)
schedule_work_on(smp_processor_id(), &data->dm_alert_work);
/*
* Don't need to lock this, since we are guaranteed to only
* run this on a single cpu at a time.
* Note also that we only update data->skb if the old and new skb
* pointers don't match. This ensures that we don't continually call
* synchornize_rcu if we repeatedly fail to alloc a new netlink message.
*/
if (skb != oskb) {
rcu_assign_pointer(data->skb, skb);
synchronize_rcu();
atomic_set(&data->dm_hit_count, dm_hit_limit);
}
}
static void send_dm_alert(struct work_struct *unused)
{
struct sk_buff *skb;
struct per_cpu_dm_data *data = &__get_cpu_var(dm_cpu_data);
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
/*
* Grab the skb we're about to send
*/
skb = data->skb;
skb = rcu_dereference_protected(data->skb, 1);
/*
* Replace it with a new one
@ -111,8 +134,10 @@ static void send_dm_alert(struct work_struct *unused)
/*
* Ship it!
*/
genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);
if (skb)
genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);
put_cpu_var(dm_cpu_data);
}
/*
@ -123,9 +148,11 @@ static void send_dm_alert(struct work_struct *unused)
*/
static void sched_send_work(unsigned long unused)
{
struct per_cpu_dm_data *data = &__get_cpu_var(dm_cpu_data);
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
schedule_work(&data->dm_alert_work);
schedule_work_on(smp_processor_id(), &data->dm_alert_work);
put_cpu_var(dm_cpu_data);
}
static void trace_drop_common(struct sk_buff *skb, void *location)
@ -134,9 +161,16 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
struct nlmsghdr *nlh;
struct nlattr *nla;
int i;
struct per_cpu_dm_data *data = &__get_cpu_var(dm_cpu_data);
struct sk_buff *dskb;
struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);
rcu_read_lock();
dskb = rcu_dereference(data->skb);
if (!dskb)
goto out;
if (!atomic_add_unless(&data->dm_hit_count, -1, 0)) {
/*
* we're already at zero, discard this hit
@ -144,7 +178,7 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
goto out;
}
nlh = (struct nlmsghdr *)data->skb->data;
nlh = (struct nlmsghdr *)dskb->data;
nla = genlmsg_data(nlmsg_data(nlh));
msg = nla_data(nla);
for (i = 0; i < msg->entries; i++) {
@ -158,7 +192,7 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
/*
* We need to create a new entry
*/
__nla_reserve_nohdr(data->skb, sizeof(struct net_dm_drop_point));
__nla_reserve_nohdr(dskb, sizeof(struct net_dm_drop_point));
nla->nla_len += NLA_ALIGN(sizeof(struct net_dm_drop_point));
memcpy(msg->points[msg->entries].pc, &location, sizeof(void *));
msg->points[msg->entries].count = 1;
@ -170,6 +204,8 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
}
out:
rcu_read_unlock();
put_cpu_var(dm_cpu_data);
return;
}
@ -375,6 +411,8 @@ static int __init init_net_drop_monitor(void)
data->send_timer.function = sched_send_work;
}
initialized = 1;
goto out;
out_unreg: