diff options
author | Kuniyuki Iwashima | 2022-10-14 11:26:25 -0700 |
---|---|---|
committer | Paolo Abeni | 2022-10-18 10:17:18 +0200 |
commit | 69421bf98482d089e50799f45e48b25ce4a8d154 (patch) | |
tree | 97fa8e200fac0b54cb97c3940a5e99c6a133ced6 /net/ipv6 | |
parent | 402fe7a5728789f3a3998d2823b7a110f4cd924e (diff) |
udp: Update reuse->has_conns under reuseport_lock.
When we call connect() for a UDP socket in a reuseport group, we have
to update sk->sk_reuseport_cb->has_conns to 1. Otherwise, the kernel
could select a unconnected socket wrongly for packets sent to the
connected socket.
However, the current way to set has_conns is illegal and possible to
trigger that problem. reuseport_has_conns() changes has_conns under
rcu_read_lock(), which upgrades the RCU reader to the updater. Then,
it must do the update under the updater's lock, reuseport_lock, but
it doesn't for now.
For this reason, there is a race below where we fail to set has_conns
resulting in the wrong socket selection. To avoid the race, let's split
the reader and updater with proper locking.
cpu1 cpu2
+----+ +----+
__ip[46]_datagram_connect() reuseport_grow()
. .
|- reuseport_has_conns(sk, true) |- more_reuse = __reuseport_alloc(more_socks_size)
| . |
| |- rcu_read_lock()
| |- reuse = rcu_dereference(sk->sk_reuseport_cb)
| |
| | | /* reuse->has_conns == 0 here */
| | |- more_reuse->has_conns = reuse->has_conns
| |- reuse->has_conns = 1 | /* more_reuse->has_conns SHOULD BE 1 HERE */
| | |
| | |- rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
| | | more_reuse)
| `- rcu_read_unlock() `- kfree_rcu(reuse, rcu)
|
|- sk->sk_state = TCP_ESTABLISHED
Note the likely(reuse) in reuseport_has_conns_set() is always true,
but we put the test there for ease of review. [0]
For the record, usually, sk_reuseport_cb is changed under lock_sock().
The only exception is reuseport_grow() & TCP reqsk migration case.
1) shutdown() TCP listener, which is moved into the latter part of
reuse->socks[] to migrate reqsk.
2) New listen() overflows reuse->socks[] and call reuseport_grow().
3) reuse->max_socks overflows u16 with the new listener.
4) reuseport_grow() pops the old shutdown()ed listener from the array
and update its sk->sk_reuseport_cb as NULL without lock_sock().
shutdown()ed TCP sk->sk_reuseport_cb can be changed without lock_sock(),
but, reuseport_has_conns_set() is called only for UDP under lock_sock(),
so likely(reuse) never be false in reuseport_has_conns_set().
[0]: https://lore.kernel.org/netdev/CANn89iLja=eQHbsM_Ta2sQF0tOGU8vAGrh_izRuuHjuO1ouUag@mail.gmail.com/
Fixes: acdcecc61285 ("udp: correct reuseport selection with connected sockets")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20221014182625.89913-1-kuniyu@amazon.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'net/ipv6')
-rw-r--r-- | net/ipv6/datagram.c | 2 | ||||
-rw-r--r-- | net/ipv6/udp.c | 2 |
2 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c index df665d4e8f0f..5ecb56522f9d 100644 --- a/net/ipv6/datagram.c +++ b/net/ipv6/datagram.c @@ -256,7 +256,7 @@ ipv4_connected: goto out; } - reuseport_has_conns(sk, true); + reuseport_has_conns_set(sk); sk->sk_state = TCP_ESTABLISHED; sk_set_txhash(sk); out: diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 8d09f0ea5b8c..129ec5a9b0eb 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -195,7 +195,7 @@ static struct sock *udp6_lib_lookup2(struct net *net, result = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum); /* Fall back to scoring if group has connections */ - if (result && !reuseport_has_conns(sk, false)) + if (result && !reuseport_has_conns(sk)) return result; result = result ? : sk; |