Patch "ipv4: Avoid crashing in ip_error" has been added to the 4.0-stable tree

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

ipv4: Avoid crashing in ip_error

to the 4.0-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:
ipv4-avoid-crashing-in-ip_error.patch
and it can be found in the queue-4.0 subdirectory.

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

From: "Eric W. Biederman" <[email protected]>
Date: Fri, 22 May 2015 04:58:12 -0500
Subject: ipv4: Avoid crashing in ip_error

From: "Eric W. Biederman" <[email protected]>

[ Upstream commit 381c759d9916c42959515ad34a6d467e24a88e93 ]

ip_error does not check if in_dev is NULL before dereferencing it.

IThe following sequence of calls is possible:
CPU A CPU B
ip_rcv_finish

    ip_route_input_noref()
        ip_route_input_slow()
                               inetdev_destroy()
    dst_input()

With the result that a network device can be destroyed while processing an input packet.

A crash was triggered with only unicast packets in flight, and
forwarding enabled on the only network device. The error condition
was created by the removal of the network device.

As such it is likely the that error code was -EHOSTUNREACH, and the action taken by ip_error (if in_dev had been accessible) would have been to not increment any counters and to have tried and likely failed to send an icmp error as the network device is going away.

Therefore handle this weird case by just dropping the packet if !in_dev. It will result in dropping the packet sooner, and will not result in an actual change of behavior.

---
 net/ipv4/route.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -903,6 +903,10 @@ static int ip_error(struct sk_buff *skb)
 	bool send;
 	int code;
 
+	/* IP on this device is disabled. */
+	if (!in_dev)
+		goto out;
+
 	net = dev_net(rt->dst.dev);
 	if (!IN_DEV_FORWARD(in_dev)) {
 		switch (rt->dst.error) {

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

queue-4.0/ipv4-avoid-crashing-in-ip_error.patch