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: Sasha Levin <sasha.levin@oracle.com>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cd0db5471bb5eb6048208404aab71253867e1eec..52d2db866965668da54c5adee6ea11cec1c063db 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1336,10 +1336,8 @@ 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 d6516910bf4126b5cbd91608d00587d06dc35233..dd530f0e5a8a29df24dbf9484c5a34a3357e6804 100644 (file)
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -514,10 +514,8 @@ 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;
 }