From: Neil Horman Date: Fri, 27 Apr 2012 10:11:49 +0000 (+0000) Subject: drop_monitor: Make updating data->skb smp safe X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=3885ca785a3618593226687ced84f3f336dc3860;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git drop_monitor: Make updating data->skb smp safe 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 Reported-by: Eric Dumazet CC: David Miller Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c index a221a5bbecf7..7592943513e3 100644 --- a/net/core/drop_monitor.c +++ b/net/core/drop_monitor.c @@ -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_on(smp_processor_id(), &data->dm_alert_work); - schedule_work(&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: