[3.19.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-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt2.

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

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 5609714e7d571d0884b02accff16f80a40982db9 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 13b4dcf..089d334 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1348,10 +1348,8 @@ 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 d953a31..daea755 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -528,10 +528,8 @@ 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