udp: fix behavior of wrong checksums

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>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index d10b7e0112ebdb8fa61c650725ae7fae68f7e669..1c92ea67baefefb801d334fe60144cbcc3af63f2 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1345,10 +1345,8 @@ 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 c2ec41617a35481d8b5b11dbae59884a0c16cbb3..e51fc3eee6dbd65506e8612fc5782b9482cf4708 100644 (file)
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -525,10 +525,8 @@ 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;
 }