[3.13.y-ckt stable] Patch "udp: fix behavior of wrong checksums" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    udp: fix behavior of wrong checksums

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt22.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From fcff4119afc3f65f0402eb78c6b6c2422eb26489 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet at google.com>
Date: Sat, 30 May 2015 09:16:53 -0700
Subject: 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 at google.com>
Cc: Willem de Bruijn <willemb at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 98ea36d..7841ffd 100644
--- 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;
 }
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 6028bc74..fbe234e 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -513,10 +513,8 @@ 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;
 }
--
1.9.1