forked from Minki/linux
69421bf984
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:
|
||
|---|---|---|
| .. | ||
| ila | ||
| netfilter | ||
| addrconf_core.c | ||
| addrconf.c | ||
| addrlabel.c | ||
| af_inet6.c | ||
| ah6.c | ||
| anycast.c | ||
| calipso.c | ||
| datagram.c | ||
| esp6_offload.c | ||
| esp6.c | ||
| exthdrs_core.c | ||
| exthdrs_offload.c | ||
| exthdrs.c | ||
| fib6_notifier.c | ||
| fib6_rules.c | ||
| fou6.c | ||
| icmp.c | ||
| inet6_connection_sock.c | ||
| inet6_hashtables.c | ||
| ioam6_iptunnel.c | ||
| ioam6.c | ||
| ip6_checksum.c | ||
| ip6_fib.c | ||
| ip6_flowlabel.c | ||
| ip6_gre.c | ||
| ip6_icmp.c | ||
| ip6_input.c | ||
| ip6_offload.c | ||
| ip6_offload.h | ||
| ip6_output.c | ||
| ip6_tunnel.c | ||
| ip6_udp_tunnel.c | ||
| ip6_vti.c | ||
| ip6mr.c | ||
| ipcomp6.c | ||
| ipv6_sockglue.c | ||
| Kconfig | ||
| Makefile | ||
| mcast_snoop.c | ||
| mcast.c | ||
| mip6.c | ||
| ndisc.c | ||
| netfilter.c | ||
| output_core.c | ||
| ping.c | ||
| proc.c | ||
| protocol.c | ||
| raw.c | ||
| reassembly.c | ||
| route.c | ||
| rpl_iptunnel.c | ||
| rpl.c | ||
| seg6_hmac.c | ||
| seg6_iptunnel.c | ||
| seg6_local.c | ||
| seg6.c | ||
| sit.c | ||
| syncookies.c | ||
| sysctl_net_ipv6.c | ||
| tcp_ipv6.c | ||
| tcpv6_offload.c | ||
| tunnel6.c | ||
| udp_impl.h | ||
| udp_offload.c | ||
| udp.c | ||
| udplite.c | ||
| xfrm6_input.c | ||
| xfrm6_output.c | ||
| xfrm6_policy.c | ||
| xfrm6_protocol.c | ||
| xfrm6_state.c | ||
| xfrm6_tunnel.c | ||