commit 3c353df4ca0f8f6912e103ca6d8d593ff4563b68
author Eric Dumazet <edumazet@google.com> Fri May 24 05:49:58 2013 +0000
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> Thu Jun 27 11:27:32 2013 -0700
tree 5ff1078bfc5a8faecb44bccd01d1711d44747efb
parent fa17eb7500ff1857fba3a01846e32c599cd332c3

ip_tunnel: fix kernel panic with icmp_dest_unreach

[ Upstream commit a622260254ee481747cceaaa8609985b29a31565 ]

Daniel Petre reported crashes in icmp_dst_unreach() with following call
graph:

Daniel found a similar problem mentioned in
 http://lkml.indiana.edu/hypermail/linux/kernel/1007.0/00961.html

And indeed this is the root cause : skb->cb[] contains data fooling IP
stack.

We must clear IPCB in ip_tunnel_xmit() sooner in case dst_link_failure()
is called. Or else skb->cb[] might contain garbage from GSO segmentation
layer.

A similar fix was tested on linux-3.9, but gre code was refactored in
linux-3.10. I'll send patches for stable kernels as well.

Many thanks to Daniel for providing reports, patches and testing !

Reported-by: Daniel Petre <daniel.petre@rcs-rds.ro>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv4/ip_gre.c

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index b57532d..a16509c 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -722,6 +722,7 @@
 		tiph = &tunnel->parms.iph;
 	}
 
+	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	if ((dst = tiph->daddr) == 0) {
 		/* NBMA tunnel */
 
@@ -865,7 +866,6 @@
 	skb_reset_transport_header(skb);
 	skb_push(skb, gre_hlen);
 	skb_reset_network_header(skb);
-	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
 			      IPSKB_REROUTED);
 	skb_dst_drop(skb);

net/ipv4/ipip.c

diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index ae1413e..d2f6348 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -448,6 +448,7 @@
 	if (tos & 1)
 		tos = old_iph->tos;
 
+	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	if (!dst) {
 		/* NBMA tunnel */
 		if ((rt = skb_rtable(skb)) == NULL) {
@@ -530,7 +531,6 @@
 	skb->transport_header = skb->network_header;
 	skb_push(skb, sizeof(struct iphdr));
 	skb_reset_network_header(skb);
-	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
 	IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED |
 			      IPSKB_REROUTED);
 	skb_dst_drop(skb);