udp: fix behavior of wrong checksums

commit beb39db59d14990e401e235faf66a6b9b31240b0 upstream.

We have two problems in UDP stack related to bogus checksums :

1) We return -EAGAIN to application even if receive queue is not empty.
   This breaks applications using edge trigger epoll()

2) Under UDP flood, we can loop forever without yielding to other
   processes, potentially hanging the host, especially on non SMP.

This patch is an attempt to make things better.

We might in the future add extra support for rt applications
wanting to better control time spent doing a recv() in a hostile
environment. For example we could validate checksums before queuing
packets in socket receive queue.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 7d5a8661df769d95e05c8214ecd5afc8f0144d26..688658dd7958dd49df6491ccfdccc59872c3bf5f 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1356,10 +1356,8 @@ csum_copy_err:
        }
        unlock_sock_fast(sk, slow);
 
-       if (noblock)
-               return -EAGAIN;
-
-       /* starting over for a new packet */
+       /* starting over for a new packet, but check if we need to yield */
+       cond_resched();
        msg->msg_flags &= ~MSG_TRUNC;
        goto try_again;
 }

diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 7092ff78fd8498e1cf84a20091b92d6c867a64e6..ad5891072a89ea1084c48393191e45d9566e62dc 100644 (file)
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -515,10 +515,8 @@ csum_copy_err:
        }
        unlock_sock_fast(sk, slow);
 
-       if (noblock)
-               return -EAGAIN;
-
-       /* starting over for a new packet */
+       /* starting over for a new packet, but check if we need to yield */
+       cond_resched();
        msg->msg_flags &= ~MSG_TRUNC;
        goto try_again;
 }