Patch "icmp: don't fail on fragment reassembly time exceeded" has been added to the 4.14-stable tree

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

icmp: don't fail on fragment reassembly time exceeded

to the 4.14-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:
icmp-don-t-fail-on-fragment-reassembly-time-exceeded.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Matteo Croce <[email protected]>
Date: Thu, 12 Oct 2017 16:12:37 +0200
Subject: icmp: don't fail on fragment reassembly time exceeded

From: Matteo Croce <[email protected]>

[ Upstream commit 258bbb1b0e594ad5f5652cb526b3c63e6a7fad3d ]

The ICMP implementation currently replies to an ICMP time exceeded message (type 11) with an ICMP host unreachable message (type 3, code 1).

However, time exceeded messages can either represent "time to live exceeded in transit" (code 0) or "fragment reassembly time exceeded" (code 1).

Unconditionally replying to "fragment reassembly time exceeded" with host unreachable messages might cause unjustified connection resets which are now easily triggered as UFO has been removed, because, in turn, sending large buffers triggers IP fragmentation.

The issue can be easily reproduced by running a lot of UDP streams which is likely to trigger IP fragmentation:

  # start netserver in the test namespace
  ip netns add test
  ip netns exec test netserver

  # create a VETH pair
  ip link add name veth0 type veth peer name veth0 netns test
  ip link set veth0 up
  ip -n test link set veth0 up

for i in $(seq 20 29); do

      # assign addresses to both ends
      ip addr add dev veth0 192.168.$i.1/24
      ip -n test addr add dev veth0 192.168.$i.2/24

      # start the traffic
      netperf -L 192.168.$i.1 -H 192.168.$i.2 -t UDP_STREAM -l 0 &
  done

  # wait
  send_data: data send error: No route to host (errno 113)
  netperf: send_omni: send_data failed: No route to host

We need to differentiate instead: if fragment reassembly time exceeded is reported, we need to silently drop the packet,
if time to live exceeded is reported, maintain the current behaviour. In both cases increment the related error count "icmpInTimeExcds".

While at it, fix a typo in a comment, and convert the if statement into a switch to mate it more readable.

---
 net/ipv4/icmp.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

@@ -782,7 +782,7 @@ static bool icmp_tag_validation(int prot
 }
 
 /*
- *	Handle ICMP_DEST_UNREACH, ICMP_TIME_EXCEED, ICMP_QUENCH, and
+ *	Handle ICMP_DEST_UNREACH, ICMP_TIME_EXCEEDED, ICMP_QUENCH, and
  *	ICMP_PARAMETERPROB.
  */
 

@@ -810,7 +810,8 @@ static bool icmp_unreach(struct sk_buff
 	if (iph->ihl < 5) /* Mangled header, drop. */
 		goto out_err;
 
-	if (icmph->type == ICMP_DEST_UNREACH) {
+	switch (icmph->type) {
+	case ICMP_DEST_UNREACH:
 		switch (icmph->code & 15) {
 		case ICMP_NET_UNREACH:
 		case ICMP_HOST_UNREACH:

@@ -846,8 +847,16 @@ static bool icmp_unreach(struct sk_buff
 		}
 		if (icmph->code > NR_ICMP_UNREACH)
 			goto out;
-	} else if (icmph->type == ICMP_PARAMETERPROB)
+		break;
+	case ICMP_PARAMETERPROB:
 		info = ntohl(icmph->un.gateway) >> 24;
+		break;
+	case ICMP_TIME_EXCEEDED:
+		__ICMP_INC_STATS(net, ICMP_MIB_INTIMEEXCDS);
+		if (icmph->code == ICMP_EXC_FRAGTIME)
+			goto out;
+		break;
+	}
 
 	/*
 	 *	Throw it at our lower layers

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/icmp-don-t-fail-on-fragment-reassembly-time-exceeded.patch