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Merge branch 'l2tp-remove-unsafe-calls-to-l2tp_tunnel_find_nth'
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Guillaume Nault says:

====================
l2tp: remove unsafe calls to l2tp_tunnel_find_nth()

Using l2tp_tunnel_find_nth() is racy, because the returned tunnel can
go away as soon as this function returns. This series introduce
l2tp_tunnel_get_nth() as a safe replacement to fixes these races.

With this series, all unsafe tunnel/session lookups are finally gone.
====================

Acked-by: Jason Wang <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
davem330 committed Apr 13, 2018
2 parents 9267c43 + f726214 commit c5042da
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Showing 5 changed files with 60 additions and 33 deletions.
40 changes: 20 additions & 20 deletions net/l2tp/l2tp_core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,26 @@ 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);

/* Lookup a session. A new reference is held on the returned session. */
struct l2tp_session *l2tp_session_get(const struct net *net,
struct l2tp_tunnel *tunnel,
Expand Down Expand Up @@ -335,26 +355,6 @@ int l2tp_session_register(struct l2tp_session *session,
}
EXPORT_SYMBOL_GPL(l2tp_session_register);

struct l2tp_tunnel *l2tp_tunnel_find_nth(const struct net *net, int nth)
{
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) {
rcu_read_unlock_bh();
return tunnel;
}
}

rcu_read_unlock_bh();

return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_find_nth);

/*****************************************************************************
* Receive data handling
*****************************************************************************/
Expand Down
3 changes: 2 additions & 1 deletion net/l2tp/l2tp_core.h
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,8 @@ 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,
Expand All @@ -220,7 +222,6 @@ struct l2tp_session *l2tp_session_get(const struct net *net,
struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth);
struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
const char *ifname);
struct l2tp_tunnel *l2tp_tunnel_find_nth(const struct net *net, int nth);

int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id,
u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
Expand Down
15 changes: 13 additions & 2 deletions net/l2tp/l2tp_debugfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,11 @@ struct l2tp_dfs_seq_data {

static void l2tp_dfs_next_tunnel(struct l2tp_dfs_seq_data *pd)
{
pd->tunnel = l2tp_tunnel_find_nth(pd->net, pd->tunnel_idx);
/* Drop reference taken during previous invocation */
if (pd->tunnel)
l2tp_tunnel_dec_refcount(pd->tunnel);

pd->tunnel = l2tp_tunnel_get_nth(pd->net, pd->tunnel_idx);
pd->tunnel_idx++;
}

Expand Down Expand Up @@ -96,7 +100,14 @@ static void *l2tp_dfs_seq_next(struct seq_file *m, void *v, loff_t *pos)

static void l2tp_dfs_seq_stop(struct seq_file *p, void *v)
{
/* nothing to do */
struct l2tp_dfs_seq_data *pd = v;

if (!pd || pd == SEQ_START_TOKEN)
return;

/* Drop reference taken by last invocation of l2tp_dfs_next_tunnel() */
if (pd->tunnel)
l2tp_tunnel_dec_refcount(pd->tunnel);
}

static void l2tp_dfs_seq_tunnel_show(struct seq_file *m, void *v)
Expand Down
11 changes: 8 additions & 3 deletions net/l2tp/l2tp_netlink.c
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Original file line number Diff line number Diff line change
Expand Up @@ -487,14 +487,17 @@ 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, L2TP_CMD_TUNNEL_GET) < 0)
tunnel, L2TP_CMD_TUNNEL_GET) < 0) {
l2tp_tunnel_dec_refcount(tunnel);
goto out;
}
l2tp_tunnel_dec_refcount(tunnel);

ti++;
}
Expand Down Expand Up @@ -848,14 +851,15 @@ 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;
}

session = l2tp_session_get_nth(tunnel, si);
if (session == NULL) {
ti++;
l2tp_tunnel_dec_refcount(tunnel);
tunnel = NULL;
si = 0;
continue;
Expand All @@ -865,6 +869,7 @@ static int l2tp_nl_cmd_session_dump(struct sk_buff *skb, struct netlink_callback
cb->nlh->nlmsg_seq, NLM_F_MULTI,
session, L2TP_CMD_SESSION_GET) < 0) {
l2tp_session_dec_refcount(session);
l2tp_tunnel_dec_refcount(tunnel);
break;
}
l2tp_session_dec_refcount(session);
Expand Down
24 changes: 17 additions & 7 deletions net/l2tp/l2tp_ppp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1551,16 +1551,19 @@ struct pppol2tp_seq_data {

static void pppol2tp_next_tunnel(struct net *net, struct pppol2tp_seq_data *pd)
{
/* Drop reference taken during previous invocation */
if (pd->tunnel)
l2tp_tunnel_dec_refcount(pd->tunnel);

for (;;) {
pd->tunnel = l2tp_tunnel_find_nth(net, pd->tunnel_idx);
pd->tunnel = l2tp_tunnel_get_nth(net, pd->tunnel_idx);
pd->tunnel_idx++;

if (pd->tunnel == NULL)
break;
/* Only accept L2TPv2 tunnels */
if (!pd->tunnel || pd->tunnel->version == 2)
return;

/* Ignore L2TPv3 tunnels */
if (pd->tunnel->version < 3)
break;
l2tp_tunnel_dec_refcount(pd->tunnel);
}
}

Expand Down Expand Up @@ -1609,7 +1612,14 @@ static void *pppol2tp_seq_next(struct seq_file *m, void *v, loff_t *pos)

static void pppol2tp_seq_stop(struct seq_file *p, void *v)
{
/* nothing to do */
struct pppol2tp_seq_data *pd = v;

if (!pd || pd == SEQ_START_TOKEN)
return;

/* Drop reference taken by last invocation of pppol2tp_next_tunnel() */
if (pd->tunnel)
l2tp_tunnel_dec_refcount(pd->tunnel);
}

static void pppol2tp_seq_tunnel_show(struct seq_file *m, void *v)
Expand Down

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