netdev - [PATCH net] ipv4: remove warning in ip_recv

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 23 May 2018 14:29:52 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net] ipv4: remove warning in ip_recv_error

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

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@...il.com>
Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 net/ipv4/ip_sockglue.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 5ad2d8ed3a3f..57bbb060faaf 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -505,8 +505,6 @@ int ip_recv_error(struct sock *sk, struct msghdr *msg, int len, int *addr_len)
 	int err;
 	int copied;

-	WARN_ON_ONCE(sk->sk_family == AF_INET6);
-
 	err = -EAGAIN;
 	skb = sock_dequeue_err_skb(sk);
 	if (!skb)
-- 
2.17.0.441.gb46fe60e1d-goog