From beb39db59d14990e401e235faf66a6b9b31240b0 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sat, 30 May 2015 09:16:53 -0700 Subject: [PATCH] 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 Cc: Willem de Bruijn Signed-off-by: David S. Miller --- net/ipv4/udp.c | 6 ++---- net/ipv6/udp.c | 6 ++---- 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index d10b7e0112ebd..1c92ea67baefe 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1345,10 +1345,8 @@ int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock, } 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 c2ec41617a354..e51fc3eee6dbd 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -525,10 +525,8 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, } 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; }