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rtnetlink: protect handler table with rcu
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Note that netlink dumps still acquire rtnl mutex via the netlink
dump infrastructure.

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Florian Westphal authored and David S. Miller committed Aug 9, 2017
1 parent 0cc0902 commit 6853dd4
Showing 1 changed file with 65 additions and 56 deletions.
121 changes: 65 additions & 56 deletions net/core/rtnetlink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -126,7 +126,7 @@ bool lockdep_rtnl_is_held(void)
EXPORT_SYMBOL(lockdep_rtnl_is_held);
#endif /* #ifdef CONFIG_PROVE_LOCKING */

static struct rtnl_link *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];
static struct rtnl_link __rcu *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];
static refcount_t rtnl_msg_handlers_ref[RTNL_FAMILY_MAX + 1];

static inline int rtm_msgindex(int msgtype)
Expand All @@ -143,36 +143,6 @@ static inline int rtm_msgindex(int msgtype)
return msgindex;
}

static rtnl_doit_func rtnl_get_doit(int protocol, int msgindex)
{
struct rtnl_link *tab;

if (protocol <= RTNL_FAMILY_MAX)
tab = rtnl_msg_handlers[protocol];
else
tab = NULL;

if (tab == NULL || tab[msgindex].doit == NULL)
tab = rtnl_msg_handlers[PF_UNSPEC];

return tab[msgindex].doit;
}

static rtnl_dumpit_func rtnl_get_dumpit(int protocol, int msgindex)
{
struct rtnl_link *tab;

if (protocol <= RTNL_FAMILY_MAX)
tab = rtnl_msg_handlers[protocol];
else
tab = NULL;

if (tab == NULL || tab[msgindex].dumpit == NULL)
tab = rtnl_msg_handlers[PF_UNSPEC];

return tab[msgindex].dumpit;
}

/**
* __rtnl_register - Register a rtnetlink message type
* @protocol: Protocol family or PF_UNSPEC
Expand Down Expand Up @@ -201,18 +171,17 @@ int __rtnl_register(int protocol, int msgtype,
BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
msgindex = rtm_msgindex(msgtype);

tab = rtnl_msg_handlers[protocol];
tab = rcu_dereference(rtnl_msg_handlers[protocol]);
if (tab == NULL) {
tab = kcalloc(RTM_NR_MSGTYPES, sizeof(*tab), GFP_KERNEL);
if (tab == NULL)
return -ENOBUFS;

rtnl_msg_handlers[protocol] = tab;
rcu_assign_pointer(rtnl_msg_handlers[protocol], tab);
}

if (doit)
tab[msgindex].doit = doit;

if (dumpit)
tab[msgindex].dumpit = dumpit;

Expand Down Expand Up @@ -249,16 +218,22 @@ EXPORT_SYMBOL_GPL(rtnl_register);
*/
int rtnl_unregister(int protocol, int msgtype)
{
struct rtnl_link *handlers;
int msgindex;

BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
msgindex = rtm_msgindex(msgtype);

if (rtnl_msg_handlers[protocol] == NULL)
rtnl_lock();
handlers = rtnl_dereference(rtnl_msg_handlers[protocol]);
if (!handlers) {
rtnl_unlock();
return -ENOENT;
}

rtnl_msg_handlers[protocol][msgindex].doit = NULL;
rtnl_msg_handlers[protocol][msgindex].dumpit = NULL;
handlers[msgindex].doit = NULL;
handlers[msgindex].dumpit = NULL;
rtnl_unlock();

return 0;
}
Expand All @@ -278,10 +253,12 @@ void rtnl_unregister_all(int protocol)
BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);

rtnl_lock();
handlers = rtnl_msg_handlers[protocol];
rtnl_msg_handlers[protocol] = NULL;
handlers = rtnl_dereference(rtnl_msg_handlers[protocol]);
RCU_INIT_POINTER(rtnl_msg_handlers[protocol], NULL);
rtnl_unlock();

synchronize_net();

while (refcount_read(&rtnl_msg_handlers_ref[protocol]) > 0)
schedule();
kfree(handlers);
Expand Down Expand Up @@ -2820,11 +2797,13 @@ static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
* traverse the list of net devices and compute the minimum
* buffer size based upon the filter mask.
*/
list_for_each_entry(dev, &net->dev_base_head, dev_list) {
rcu_read_lock();
for_each_netdev_rcu(net, dev) {
min_ifinfo_dump_size = max_t(u16, min_ifinfo_dump_size,
if_nlmsg_size(dev,
ext_filter_mask));
}
rcu_read_unlock();

return nlmsg_total_size(min_ifinfo_dump_size);
}
Expand All @@ -2836,19 +2815,29 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)

if (s_idx == 0)
s_idx = 1;

for (idx = 1; idx <= RTNL_FAMILY_MAX; idx++) {
int type = cb->nlh->nlmsg_type-RTM_BASE;
struct rtnl_link *handlers;
rtnl_dumpit_func dumpit;

if (idx < s_idx || idx == PF_PACKET)
continue;
if (rtnl_msg_handlers[idx] == NULL ||
rtnl_msg_handlers[idx][type].dumpit == NULL)

handlers = rtnl_dereference(rtnl_msg_handlers[idx]);
if (!handlers)
continue;

dumpit = READ_ONCE(handlers[type].dumpit);
if (!dumpit)
continue;

if (idx > s_idx) {
memset(&cb->args[0], 0, sizeof(cb->args));
cb->prev_seq = 0;
cb->seq = 0;
}
if (rtnl_msg_handlers[idx][type].dumpit(skb, cb))
if (dumpit(skb, cb))
break;
}
cb->family = idx;
Expand Down Expand Up @@ -4151,11 +4140,12 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
struct netlink_ext_ack *extack)
{
struct net *net = sock_net(skb->sk);
struct rtnl_link *handlers;
int err = -EOPNOTSUPP;
rtnl_doit_func doit;
int kind;
int family;
int type;
int err;

type = nlh->nlmsg_type;
if (type > RTM_MAX)
Expand All @@ -4173,23 +4163,40 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
if (kind != 2 && !netlink_net_capable(skb, CAP_NET_ADMIN))
return -EPERM;

if (family > ARRAY_SIZE(rtnl_msg_handlers))
family = PF_UNSPEC;

rcu_read_lock();
handlers = rcu_dereference(rtnl_msg_handlers[family]);
if (!handlers) {
family = PF_UNSPEC;
handlers = rcu_dereference(rtnl_msg_handlers[family]);
}

if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {
struct sock *rtnl;
rtnl_dumpit_func dumpit;
u16 min_dump_alloc = 0;

rtnl_lock();
dumpit = READ_ONCE(handlers[type].dumpit);
if (!dumpit) {
family = PF_UNSPEC;
handlers = rcu_dereference(rtnl_msg_handlers[PF_UNSPEC]);
if (!handlers)
goto err_unlock;

dumpit = rtnl_get_dumpit(family, type);
if (dumpit == NULL)
goto err_unlock;
dumpit = READ_ONCE(handlers[type].dumpit);
if (!dumpit)
goto err_unlock;
}

refcount_inc(&rtnl_msg_handlers_ref[family]);

if (type == RTM_GETLINK)
min_dump_alloc = rtnl_calcit(skb, nlh);

__rtnl_unlock();
rcu_read_unlock();

rtnl = net->rtnl;
{
struct netlink_dump_control c = {
Expand All @@ -4202,18 +4209,20 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
return err;
}

rtnl_lock();
doit = rtnl_get_doit(family, type);
if (doit == NULL)
goto err_unlock;
rcu_read_unlock();

err = doit(skb, nlh, extack);
rtnl_lock();
handlers = rtnl_dereference(rtnl_msg_handlers[family]);
if (handlers) {
doit = READ_ONCE(handlers[type].doit);
if (doit)
err = doit(skb, nlh, extack);
}
rtnl_unlock();

return err;

err_unlock:
rtnl_unlock();
rcu_read_unlock();
return -EOPNOTSUPP;
}

Expand Down

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