[PATCH 4.4 13/24] ipv4: remove warning in ip_recv_error

Greg Kroah-Hartman
2018-06-12T17:03:33Z

From: Willem de Bruijn <willemb@google.com>

[ Upstream commit 730c54d59403658a62af6517338fa8d4922c1b28 ]

A precondition check in ip_recv_error triggered on an otherwise benign
race. Remove the warning.

The warning triggers when passing an ipv6 socket to this ipv4 error
handling function. RaceFuzzer was able to trigger it due to a race
in setsockopt IPV6_ADDRFORM.

---
CPU0
do_ipv6_setsockopt
sk->sk_socket->ops = &inet_dgram_ops;

---
CPU1
sk->sk_prot->recvmsg
udp_recvmsg
ip_recv_error
WARN_ON_ONCE(sk->sk_family == AF_INET6);

---
CPU0
do_ipv6_setsockopt
sk->sk_family = PF_INET;

This socket option converts a v6 socket that is connected to a v4 peer
to an v4 socket. It updates the socket on the fly, changing fields in
sk as well as other structs. This is inherently non-atomic. It races
with the lockless udp_recvmsg path.

No other code makes an assumption that these fields are updated
atomically. It is benign here, too, as ip_recv_error cares only about
the protocol of the skbs enqueued on the error queue, for which
sk_family is not a precise predictor (thanks to another isue with
IPV6_ADDRFORM).

Link: http://lkml.kernel.org/r/20180518120826.GA19515@dragonet.kaist.ac.kr
Fixes: 7ce875e5ecb8 ("ipv4: warn once on passing AF_INET6 socket to ip_recv_error")
Reported-by: DaeRyong Jeong <threeearcat@gmail.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_sockglue.c | 2 --
1 file changed, 2 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -493,8 +493,6 @@ int ip_recv_error(struct sock *sk, struc
int err;
int copied;

- WARN_ON_ONCE(sk->sk_family == AF_INET6);
-
err = -EAGAIN;
skb = sock_dequeue_err_skb(sk);
if (!skb)