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l2tp: hold reference on tunnels in netlink dumps 

commit 5846c131c39b6d0add36ec19dc8650700690f930 upstream.

l2tp_tunnel_find_nth() is unsafe: no reference is held on the returned
tunnel, therefore it can be freed whenever the caller uses it.
This patch defines l2tp_tunnel_get_nth() which works similarly, but
also takes a reference on the returned tunnel. The caller then has to
drop it after it stops using the tunnel.

Convert netlink dumps to make them safe against concurrent tunnel
deletion.

Fixes: 309795f4be ("l2tp: Add netlink control API for L2TP")
Change-Id: If625d89d841fa7e37794415dca0e0122374e8d60
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Guillaume Nault 2018-04-12 20:50:33 +02:00 committed by L R
parent 6dfb6c988a
commit 104fe54350
3 changed files with 30 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
net/l2tp/l2tp_core.c
View File

@ -224,6 +224,26 @@ struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get);
struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth)
{
const struct l2tp_net *pn = l2tp_pernet(net);
struct l2tp_tunnel *tunnel;
int count = 0;
rcu_read_lock_bh();
list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
if (++count > nth) {
l2tp_tunnel_inc_refcount(tunnel);
rcu_read_unlock_bh();
return tunnel;
}
}
rcu_read_unlock_bh();
return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get_nth);
/* Like l2tp_session_find() but takes a reference on the returned session.
* Optionally calls session->ref() too if do_ref is true.
*/

2
net/l2tp/l2tp_core.h
View File

@ -223,6 +223,8 @@ static inline void *l2tp_session_priv(struct l2tp_session *session)
}
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth);
void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);
struct l2tp_session *l2tp_session_get(const struct net *net,

11
net/l2tp/l2tp_netlink.c
View File

@ -384,14 +384,17 @@ static int l2tp_nl_cmd_tunnel_dump(struct sk_buff *skb, struct netlink_callback
struct net *net = sock_net(skb->sk);
for (;;) {
tunnel = l2tp_tunnel_find_nth(net, ti);
tunnel = l2tp_tunnel_get_nth(net, ti);
if (tunnel == NULL)
goto out;
if (l2tp_nl_tunnel_send(skb, NETLINK_CB(cb->skb).portid,
cb->nlh->nlmsg_seq, NLM_F_MULTI,
tunnel) <= 0)
tunnel) <= 0) {
l2tp_tunnel_dec_refcount(tunnel);
goto out;
}
l2tp_tunnel_dec_refcount(tunnel);
ti++;
}
@ -739,7 +742,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
for (;;) {
if (tunnel == NULL) {
tunnel = l2tp_tunnel_find_nth(net, ti);
tunnel = l2tp_tunnel_get_nth(net, ti);
if (tunnel == NULL)
goto out;
}
@ -747,6 +750,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
session = l2tp_session_get_nth(tunnel, si, false);
if (session == NULL) {
ti++;
l2tp_tunnel_dec_refcount(tunnel);
tunnel = NULL;
si = 0;
continue;
@ -756,6 +760,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
cb->nlh->nlmsg_seq, NLM_F_MULTI,
session) <= 0) {
l2tp_session_dec_refcount(session);
l2tp_tunnel_dec_refcount(tunnel);
break;
}
l2tp_session_dec_refcount(session);