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[PATCH 3.16.y-ckt 39/71] udp: fix behavior of wrong checksums

From Luis Henriques <luis.henriques@canonical.com>
Newsgroups linux.kernel
Subject [PATCH 3.16.y-ckt 39/71] udp: fix behavior of wrong checksums
Date 2015-06-25 12:20 +0200
Message-ID <pFcqf-5Nm-45@gated-at.bofh.it> (permalink)
References <pFcgx-5Bx-7@gated-at.bofh.it>
Organization linux.* mail to news gateway

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3.16.7-ckt14 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

commit beb39db59d14990e401e235faf66a6b9b31240b0 upstream.

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: Luis Henriques <luis.henriques@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 7d5a8661df76..688658dd7958 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1356,10 +1356,8 @@ 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 7092ff78fd84..ad5891072a89 100644
--- 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;
 }
--
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[3.16.y-ckt stable] Linux 3.16.7-ckt14 stable review Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:10 +0200
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  [PATCH 3.16.y-ckt 55/71] pata_octeon_cf: fix broken build Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:10 +0200
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  [PATCH 3.16.y-ckt 67/71] crypto: caam - improve initalization for context state saves Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:10 +0200
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  [PATCH 3.16.y-ckt 59/71] mm/memory_hotplug.c: set zone->wait_table to null after freeing it Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:10 +0200
  [PATCH 3.16.y-ckt 66/71] crypto: caam - fix uninitialized state->buf_dma field Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:10 +0200
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  [PATCH 3.16.y-ckt 35/71] net: dp83640: fix broken calibration routine. Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 36/71] net: dp83640: reinforce locking rules. Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
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  [PATCH 3.16.y-ckt 38/71] xen/netback: Properly initialize credit_bytes Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 27/71] xfrm: fix a race in xfrm_state_lookup_byspi Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 42/71] bridge: disable softirqs around br_fdb_update to avoid lockup Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 39/71] udp: fix behavior of wrong checksums Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
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  [PATCH 3.16.y-ckt 40/71] xen: netback: read hotplug script once at start of day. Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
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  [PATCH 3.16.y-ckt 33/71] net: core: Correct an over-stringent device loop detection. Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 34/71] net: phy: Allow EEE for all RGMII variants Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 32/71] arch/x86/kvm/mmu.c: work around gcc-4.4.4 bug Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 18/71] x86/asm/irq: Stop relying on magic JMP behavior for early_idt_handlers Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 48/71] Drivers: hv: vmbus: Add support for VMBus panic notifier handler Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
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  [PATCH 3.16.y-ckt 26/71] MIPS: Fix enabling of DEBUG_STACKOVERFLOW Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200
  [PATCH 3.16.y-ckt 45/71] Btrfs: send, don't leave without decrementing clone root's send_progress Luis Henriques <luis.henriques@canonical.com> - 2015-06-25 12:20 +0200

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