Patch "udp: fix behavior of wrong checksums" has been added to the 3.14-stable tree

Patch "udp: fix behavior of wrong checksums" has been added to the 3.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    udp: fix behavior of wrong checksums

to the 3.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     udp-fix-behavior-of-wrong-checksums.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Sat Jun 13 09:49:06 PDT 2015
From: Eric Dumazet <edumazet@google.com>
Date: Sat, 30 May 2015 09:16:53 -0700
Subject: udp: fix behavior of wrong checksums

From: Eric Dumazet <edumazet@google.com>

[ 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>
---
 net/ipv4/udp.c |    6 ++----
 net/ipv6/udp.c |    6 ++----
 2 files changed, 4 insertions(+), 8 deletions(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1317,10 +1317,8 @@ 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;
 }
--- 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;
 }


Patches currently in stable-queue which might be from edumazet@google.com are

queue-3.14/net_sched-invoke-attach-after-setting-dev-qdisc.patch
queue-3.14/udp-fix-behavior-of-wrong-checksums.patch
queue-3.14/tcp-ipv6-fix-flow-label-setting-in-time_wait-state.patch
queue-3.14/ipv4-avoid-crashing-in-ip_error.patch