udp: fix behavior of wrong checksums

[ Upstream commit beb39db59d14990e401e235faf66a6b9b31240b0 ]

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c3075b552248b5853f642aed19f0a89d199cb7b0..63b536bbf0b01e46bb66b60ca0976fe9bd1c13f0 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1293,10 +1293,8 @@ 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 6b298dc614e3d2d926d4962d93d3d5d52fdeb251..7e39018934137e512702b9be8aecc60dc7d2e44f 100644 (file)
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -494,10 +494,8 @@ 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;
 }