* [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock
@ 2022-08-23 10:14 Jakub Sitnicki
2022-08-25 10:23 ` Paolo Abeni
0 siblings, 1 reply; 3+ messages in thread
From: Jakub Sitnicki @ 2022-08-23 10:14 UTC (permalink / raw)
To: netdev
Cc: kernel-team, David S. Miller, Eric Dumazet, Jakub Kicinski,
Paolo Abeni, Tom Parkin, Haowei Yan
sk->sk_user_data has multiple users, which are not compatible with each
other. Writers must synchronize by grabbing the sk->sk_callback_lock.
l2tp currently fails to grab the lock when modifying the underlying tunnel
socket. Fix it by adding appropriate locking.
We don't to grab the lock when l2tp clears sk_user_data, because it happens
only in sk->sk_destruct, when the sock is going away.
v3:
- switch from sock lock to sk_callback_lock
- document write-protection for sk_user_data
v2:
- update Fixes to point to origin of the bug
- use real names in Reported/Tested-by tags
Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
Reported-by: Haowei Yan <g1042620637@gmail.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
include/net/sock.h | 2 +-
net/l2tp/l2tp_core.c | 17 +++++++++++------
2 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h
index d08cfe190a78..601c48601496 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -323,7 +323,7 @@ struct sk_filter;
* @sk_tskey: counter to disambiguate concurrent tstamp requests
* @sk_zckey: counter to order MSG_ZEROCOPY notifications
* @sk_socket: Identd and reporting IO signals
- * @sk_user_data: RPC layer private data
+ * @sk_user_data: RPC layer private data. Write-protected by @sk_callback_lock.
* @sk_frag: cached page frag
* @sk_peek_off: current peek_offset value
* @sk_send_head: front of stuff to transmit
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 7499c51b1850..429ad9633f13 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1469,16 +1469,18 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
sock = sockfd_lookup(tunnel->fd, &ret);
if (!sock)
goto err;
-
- ret = l2tp_validate_socket(sock->sk, net, tunnel->encap);
- if (ret < 0)
- goto err_sock;
}
+ sk = sock->sk;
+ write_lock(&sk->sk_callback_lock);
+
+ ret = l2tp_validate_socket(sk, net, tunnel->encap);
+ if (ret < 0)
+ goto err_sock;
+
tunnel->l2tp_net = net;
pn = l2tp_pernet(net);
- sk = sock->sk;
sock_hold(sk);
tunnel->sock = sk;
@@ -1504,7 +1506,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
setup_udp_tunnel_sock(net, sock, &udp_cfg);
} else {
- sk->sk_user_data = tunnel;
+ rcu_assign_sk_user_data(sk, tunnel);
}
tunnel->old_sk_destruct = sk->sk_destruct;
@@ -1518,6 +1520,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
if (tunnel->fd >= 0)
sockfd_put(sock);
+ write_unlock(&sk->sk_callback_lock);
return 0;
err_sock:
@@ -1525,6 +1528,8 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
sock_release(sock);
else
sockfd_put(sock);
+
+ write_unlock(&sk->sk_callback_lock);
err:
return ret;
}
--
2.37.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock
2022-08-23 10:14 [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock Jakub Sitnicki
@ 2022-08-25 10:23 ` Paolo Abeni
2022-08-26 8:32 ` Jakub Sitnicki
0 siblings, 1 reply; 3+ messages in thread
From: Paolo Abeni @ 2022-08-25 10:23 UTC (permalink / raw)
To: Jakub Sitnicki, netdev
Cc: kernel-team, David S. Miller, Eric Dumazet, Jakub Kicinski,
Tom Parkin, Haowei Yan
hello,
On Tue, 2022-08-23 at 12:14 +0200, Jakub Sitnicki wrote:
> sk->sk_user_data has multiple users, which are not compatible with each
> other. Writers must synchronize by grabbing the sk->sk_callback_lock.
>
> l2tp currently fails to grab the lock when modifying the underlying tunnel
> socket. Fix it by adding appropriate locking.
>
> We don't to grab the lock when l2tp clears sk_user_data, because it happens
> only in sk->sk_destruct, when the sock is going away.
l2tp can additionally clears sk_user_data in sk->sk_prot->close() via
udp_lib_close() -> sk_common_release() -> sk->sk_prot->destroy() ->
udp_destroy_sock() -> up->encap_destroy() -> l2tp_udp_encap_destroy().
That still happens at socket closing time, but when network has still
access to the sock itself. It should be safe as the other sk_user_data
users touch it only via fd, but perhaps a 'better safe the sorry'
approach could be relevant there?
Thanks!
Paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock
2022-08-25 10:23 ` Paolo Abeni
@ 2022-08-26 8:32 ` Jakub Sitnicki
0 siblings, 0 replies; 3+ messages in thread
From: Jakub Sitnicki @ 2022-08-26 8:32 UTC (permalink / raw)
To: Paolo Abeni
Cc: netdev, kernel-team, David S. Miller, Eric Dumazet,
Jakub Kicinski, Tom Parkin, Haowei Yan
On Thu, Aug 25, 2022 at 12:23 PM +02, Paolo Abeni wrote:
> hello,
>
> On Tue, 2022-08-23 at 12:14 +0200, Jakub Sitnicki wrote:
>> sk->sk_user_data has multiple users, which are not compatible with each
>> other. Writers must synchronize by grabbing the sk->sk_callback_lock.
>>
>> l2tp currently fails to grab the lock when modifying the underlying tunnel
>> socket. Fix it by adding appropriate locking.
>>
>> We don't to grab the lock when l2tp clears sk_user_data, because it happens
>> only in sk->sk_destruct, when the sock is going away.
>
> l2tp can additionally clears sk_user_data in sk->sk_prot->close() via
> udp_lib_close() -> sk_common_release() -> sk->sk_prot->destroy() ->
> udp_destroy_sock() -> up->encap_destroy() -> l2tp_udp_encap_destroy().
>
> That still happens at socket closing time, but when network has still
> access to the sock itself. It should be safe as the other sk_user_data
> users touch it only via fd, but perhaps a 'better safe the sorry'
> approach could be relevant there?
Fair point. Let me add that.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-08-26 8:32 UTC | newest]
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2022-08-23 10:14 [PATCH net v3] l2tp: Serialize access to sk_user_data with sk_callback_lock Jakub Sitnicki
2022-08-25 10:23 ` Paolo Abeni
2022-08-26 8:32 ` Jakub Sitnicki
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